Education for all in action: Measuring teachers’ competences for inclusive education

RESEARCH ARTICLE Education for all in action: Measuring teachers’ competences for inclusive education Wendelien VantieghemID1*, Iris Roose2, Karin Goosen1, Wouter Schelfhout3, Piet Van Avermaet1 1 Centre for Diversity & Learning, Ghent University, Ghent, Belgium, 2 Human & society, Artevelde University College, Ghent, Belgium, 3 Antwerp School of Education, University of Antwerp, Antwerpen, Belgium * wendelien.vantieghem@ugent.be Abstract While inclusive education has achieved international importance, there is no valid instru- ment to measure teachers’ competences in creating quality classrooms for diverse learners, which this study aims to remedy. Exploratory and confirmatory factor analyses with 975 pre- service teachers and 600 in-service teachers were used. Central to teachers’ inclusive teaching competency is both beliefs and efficacy. Results show that teachers hold profes- sional beliefs on student diversity, organized in four factors mapping unto axes of diversity (specifically ethnicity, disability, SES, and gender & sexuality). Teachers also hold beliefs on the responsibility of the educational field to create inclusion, organized in three factors: gen- eral school policy, initiatives geared specifically towards ethnic minority students, and initia- tives for students with a disability. Furthermore, the results show five factors related to self- efficacy: noticing student diversity, enabling high-quality student-interactions, creating stim- ulating learning environments, collaborating with colleagues and diverse parents. The facto-

rial structure and scale-scores are discussed for what they unveil of teachers’ thinking about diversity in the classroom. Introduction Nowadays, due to the expansion of education, migration flows, and various policy initiatives, classrooms are becoming increasingly diverse [1,2]. At the same time, the pursuit of inclusive education is influencing policy agendas of countries across the globe [3,4]. While inclusion was initially focused on groups traditionally occupying a marginalized position in education (including students with disabilities, from ethnic minority descent or low-SES families), inclu- sive education is currently conceptualised as a call to transform educational systems at large to reach all students regardless of their background [for a detailed discussion of the evolution of the concept of inclusive education, see 5]. This perspective on inclusion explicitly starts from a social justice standpoint and is known as Education for All (EfA) [6]. Important within this view is the recognition of the educational fields’ responsibility to take into account differences between learners in order to create qualitative learning environments for everyone, while PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 1 / 22 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Vantieghem W, Roose I, Goosen K, Schelfhout W, Van Avermaet P (2023) Education for all in action: Measuring teachers’ competences for inclusive education. PLoS ONE 18(11): e0291033. https://doi.org/10.1371/journal. pone.0291033

Editor: Pieter-Paul Verhaeghe, Vrije Universiteit Brussel, BELGIUM Received: November 28, 2022 Accepted: August 18, 2023 Published: November 8, 2023 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0291033 Copyright: © 2023 Vantieghem et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: The datasets used in the research have been made publicly available via Zenodo. A reference to these datasets is included in the Methodology: Sample & respondents; and the

maintaining a clear understanding of how systemic inequalities in education disproportionally affect specific (groups of) students [7]. EfA can be framed as a so-called wicked problem [8], being a social problem that is both hard to grasp and solve. Wicked problems are characterised by institutional complexity requir- ing cooperation and changes to several processes, while scientific knowledge on the topic is often fragmented or contested [9,10]. While effective EfA would require changes to curricula, teacher mindsets and behaviour, and cooperation between educational stakeholders (i.e., insti- tutional complexity) [11], most research on EfA employs a narrow focus by considering only one specific diversity group, and is either literature-based or qualitative in nature [12]. While this research has highlighted the crucial role of teachers and has given us some hints on how EfA can be realised, these have not been empirically tested on a large scale due to the lack of valid measurement instruments. Consequently, this article provides insight into the validation of the “DIversity SCreening in educatiOn" (DISCO)-instrument, which is an instrument designed to grasp teachers’ competences for inclusive education, and which could help both research and practice move forward in tackling EfA as a wicked problem. Teachers’ competences in inclusive education Inclusive teaching has become an obligatory professional competence for teachers in many countries [3]. Unfortunately, teachers both in Flanders and abroad express a low capacity to

address the educational needs of diverse pupils [13,14]. Hence, research that provides more insight on teachers’ competences for inclusion and the contexts in which these competences can flourish, is sorely needed. Teacher competence for inclusive education is defined as being a complex combination of knowledge, skills and attitudes that allow a teacher to successfully respond to pupils’ diversity in the classroom [15]. However, it has to be recognized that devel- oping instruments to grasp teachers’ inclusive competences is not an easy task, due to the com- plex nature of the concept of inclusive education, which entails both a broad scope (i.e., not being focused on one specific group but rather transcending any diversity group), and shows institutional complexity by requiring several educational processes at once to realize maximal learning and developmental outcomes for students [16]. Furthermore, the concept of compe- tence itself has been extensively debated as well. While some researchers have defined compe- tence as actual behaviour in real-world situations, it has been suggested that more can be learned by considering competences as a process which results in observable behaviour while simultaneously acknowledging underlying factors such as knowledge and motivation that underpin and affect this behaviour. Hence, Blo¨meke, Gustafsson (17) propose to view compe- tences along a continuum with dispositions (such as knowledge and beliefs) and performance being connected through situation-specific skills. These situation-specific skills then entail

processes such as perception and decision-making, which determine in a specific situation how dispositions are translated into performance [17,18]. As such, these situation-specific skills are akin to the concept of self-efficacy from social cognitive theory, which proposes that human achievement is dependent on one’s behaviours, internal personal factors (such as cog- nitions and beliefs) and environmental conditions [19,20], and is defined as people’s beliefs in their own capability to perform certain tasks [19]. Consequently, in order to get a broad image of aspects central to teachers’ competences for inclusive education, research is needed that combines an investigation of teachers’ beliefs on diverse learners (i.e., the scope of inclusive education) as well as self-efficacy, which in the context of inclusive education refers to teachers’ assessment of their capabilities to create the educational preconditions necessary for students’ maximal learning. Both aspects, being beliefs on diversity and sense of self-efficacy, will be dis- cussed in detail below. PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 2 / 22 DOI’s associated with the datasets are DOI: 10. 5281/zenodo.8318520 for the dataset with the pre- service teachers and DOI 10.5281/zenodo.8318572 for the dataset with the in-service teachers. Funding: Published with support from the University Foundation (Universitaire stichting) of Belgium to WV. Competing interests: The authors have declared

that no competing interests exist.

Teachers’ beliefs With regard to teachers’ beliefs on diverse learners, two distinct but related aspects are central, namely teachers’ professional beliefs on student diversity and teachers’ beliefs about the responsibility of education towards diverse learners. With regard to the latter, teachers’ view on whether equity is part of the central aims of education and hence, what constitutes the responsibilities of teachers and schools, has a profound impact on shaping their classroom behaviour [21]. However, a meta-review of research in-between 1980 and 2015 shows that teachers tend to report more negative attitudes towards inclusive education than either pupils or parents [4], while a qualitative study shows that teachers who consider it to be the responsi- bility of education to achieve both excellence and equal learning opportunities, tend to devote themselves more completely to realizing quality classes and supporting struggling students from diverse backgrounds [22]. In short, the degree in which teachers consider providing EfA as one of the educational context’s central responsibilities, will be central in shaping their will- ingness to invest time and effort in the creation of inclusive classrooms. Interestingly, respon- sibility of teachers cannot only be assessed with regard to learners, but also regarding colleagues and parents [23]. Research suggests that schools with strong parent-teacher connec- tions are better at realizing maximal developmental chances for their students [11], and that

achieving equitable learning environments requires a shared responsibility and collaboration among teachers [24]. Consequently, in order to really grasp teachers’ competences in creating inclusive education, collaboration with these partners should not be disregarded. Secondly, teachers’ beliefs on learners from diverse backgrounds is of central importance as well, called teachers’ professional beliefs about diversity [25]. These beliefs subconsciously influence teacher behaviour, for instance by involving students for whom teacher have lower expectations less actively in classroom activities or by seeing poor performance as normal [26,27]. This process has a negative impact on both students’ cognitive outcomes and well- being [28]. Importantly, such effects of teacher expectations tend to be especially powerful for at-risk students, such as students from lower socioeconomic backgrounds and ethnic minority descent [26]. Hence, in the framework of inclusive education, it is particularly important to understand and assess teachers’ beliefs on teaching diverse learners, to counter the negative self-fulfilling prophecies for these students. Unfortunately, research on teachers’ beliefs towards diverse learners often employs a narrow definition of diversity, for instance by focus- ing only on teachers’ multicultural beliefs [e.g., 29], or beliefs on students with behavioural dif- ficulties [e.g., 30]. While such specific beliefs allow for a fine-grained analysis of educational barriers for particular student groups, it remains unclear how teachers’ beliefs towards several

groups of students relate to each other and whether an overall inclusive mindset among teach- ers exists. Consequently, to fundamentally advance the research on classrooms that are effec- tive for all students, research must consider teacher beliefs towards several groups of students simultaneously. Hence, we propose to assess teachers’ beliefs on diverse learners by assessing 1) teachers’ professional beliefs towards students along important axes of diversity (i.e., ethnicity, disabil- ity, gender & sexual orientation, and socio-economic status) and 2) teachers’ beliefs on educa- tional responsibility with regards to diverse students, parents and colleagues. Teachers’ sense of efficacy In order to realise the maximal learning and developmental outcomes suggested within EfA, inclusion cannot be relegated to the side-lines as being something that some teachers some- times do within the context of specific courses or lessons, or something that only expert teach- ers do after having achieved mastery in “general” teaching tasks aimed at “regular” students PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 3 / 22

[31]. Rather, it becomes an inclusive culture that all teachers adhere to in the classroom [6], and which requires a constant effort of teachers to continuously monitor, evaluate and adapt their teaching methods to best suit the needs of the students present [32]. In such an endeav- our, self-efficacy could constitute a powerful resource, as self-efficacy beliefs have proven to be powerful predictors of teachers’ motivation and actual performance [33], with a high sense of self-efficacy being especially powerful in the face of adversity in order to persevere when faced with difficulties or failure [19]. Importantly, research has shown that self-efficacy is not unidimensional, but tends to be context- and task-specific [34]. Consequently, it is important to consider teachers’ self-efficacy with regards to several necessary tasks to create inclusive classroom environments rather than one overall assessment. At the same time, it remains important to employ a broad definition of diversity in order to truly capture EfA and the intersectionally diverse nature of classroom con- texts nowadays, rather than narrowing the focus to a specific diversity group (note that such teaching self-efficacy scales do exist, such as the ones focused on ethnic diversity developed by Siwatu [35] or Romijn, Slot [36], or focused on students with a disability by Sharma, Loreman [37]). Hence, in this research, teachers’ self-efficacy beliefs with respect to several central aspects of realizing inclusive learning environments will be assessed. That is: 1) noticing diver-

sity, 2) creating powerful learning environments for diverse students, and 3) realizing positive classroom interactions for diverse students. The first subcomponent of noticing diversity, taps the extent to which teachers see themselves capable of actively gathering information on sev- eral aspects of student diversity (f.i., students’ background, interests, well-being, . . .). Only when teachers are aware of and exploit these differences, can a classroom environment be maximally adapted to the strengths and needs of every student [38]. In tandem with this notic- ing, the second subcomponent taps the extent to which teachers feel capable to design a class- room environment that takes into account the strengths and needs of their students. The third subcomponent measures the extent to which teachers feel capable to create positive classroom climates for their students, since research has shown both the impact teachers have on the cre- ation of qualitative relationships among students [39] as well as the vital importance of this for at-risk students’ well-being and achievement [40]. Note that by delineating these aspects, this paper does not explicitly follow the oft-used distinction in teachers’ self-efficacy research in- between instructional strategies, classroom organisation and student engagement [41,42]. This choice was fuelled by researchers noting that EfA does not necessarily require new teaching practices, but rather an awareness of diversity and a goal-orientation towards equitable learn-

ing opportunities in what teachers do [6,43]. For instance, within the aspect of positive class- room interactions can cooperative learning be linked to both student engagement and instructional strategies [44]. Hence, we felt that an instrument designed to grasp teachers’ effi- cacy for inclusive education would be better served by recognizing this complex intermingling of goals and methods rather than a strict distinction in-between instructional strategies, class- room organisation and student engagement. As discussed above, there is currently a lack of valid instruments to grasp teachers’ compe- tence for inclusive education, due to the institutional complexity and broad scope of EfA. That is, to truly capture competence for EfA, researchers require an instrument that considers both teachers willingness to work on inclusion (i.e., beliefs) as well as their perceived capabilities to create inclusive learning environment (i.e., self-efficacy). Furthermore, existing instruments tend to focus on either a specific teaching sub-component, such as class management or differ- entiated instruction, or on a specific student group, such as students with a disability or ethnic minority background, while EfA transcends specific diversity groups and encompasses several educational processes necessary for maximal learning outcomes. Hence, the goal of this article is to establish a valid and reliable instrument to measure teachers’ beliefs and self-efficacy with PLOS ONE Measuring teachers’ competences for inclusive education

PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 4 / 22

regards to inclusive education. Furthermore, teachers’ scale-scores on this validated instru- ment are analysed in order to gain insight on teachers’ thinking about diversity in the classroom. Methodology Sample & respondents In order to allow for a process of trial and improvement as well as cross-validation, data was collected in two steps within Flanders (Belgium). In the first step, data was collected among pre-service teachers. Based on the exploratory factor analyses on this data, the survey was opti- mised and then tested again in the second step. During this second step, data from a new sam- ple consisting of in-service teachers was analysed using confirmatory factor analyses (for more information, see Plan of analysis). In the first step, data was collected among pre-service teach- ers in the fall of 2017 in a sample of teacher education institutions [45]. All teacher education institutions within a Flemish province were invited to participate. Seven of the eight institu- tions decided to participate in the study (participation rate = 87.5%), translating to a total number of 975 pre-service teachers filling out the online research instruments. Of these, 167 students were in training to become a nursery teacher, 155 were studying to become primary school teachers, whereas 143 and 433 were studying to become respectively lower or higher secondary school teachers. 75% of the sample were women, while the mean age was 27.38 with a range from 17 to 57. By the end of the survey, 647 students had provided valid answers, trans- lating to an attrition rate of 33.6%.

In the second step, data was collected with in-service teachers in the spring of 2018 [46]. All schools within one Flemish city were invited to participate. Of the 40 contacted schools, 28 participated in the study, translating to a participation rate of 70%. All teachers within each school were invited to fill out the online survey (N = 600). Of these, 213 were working in a pri- mary school, while 384 were situated in a secondary school (with 3 people providing no answer to this question). 73.2% of the sample were women, while the mean age was 41.02 with a range from 22 to 63. When comparing the data to previous descriptions of the Flemish teaching pop- ulation [47,48], we see a congruence for both age and gender divisions, indicating that no sys- tematic biases seem to have occurred. By the end of the survey, 520 respondents provided valid answers, translating to an attrition rate of 13.3%. Due to the anonymous and non-invasive nature of the research (being a voluntary, one- time participation of adults in survey-research on professional practice), no official approval by the ethics committee was sought. Following the European Code of Conduct for Research Integrity, all respondents agreed to a written informed consent stating that participation in the research was voluntary, that they could stop their participation at any moment, and that their answers would be processed anonymously. Instrument Item creation and selection. First, a pool of items was created by three researchers with expert knowledge on diversity in education. In order to maintain the goals of the DISCO-

instrument and reflect the central tenets of EfA, the following criteria were observed during this creation phase: (1) to mitigate the fragmentation of the EfA field and employ a broad defi- nition of diversity, items had to either be applicable to all children or refer to specific diversity groups in a balanced way; (2) items needed to explicitly measure a single practice or percep- tion; and (3) items needed to be relevant across multiple teaching contexts; this implied that items had to be recognisable for teachers across different teaching levels, including primary and secondary education; that items had to refer to actions that could be performed by all PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 5 / 22

teachers, and not just those teaching specific courses or students; and had to refer to actions pertaining to day-to-day teaching activities in order to reflect the continuous nature of work- ing on inclusion. For the wording of the items, the brainstorm was based on an existing reflec- tion-instrument for how teachers address diversity in the classroom, and validated scales on ethnocentrism, homonegativity, differentiation, collaboration, and teaching efficacy. In order to ensure content validity and readability, these items were then adapted based on feedback by two academics in the field of diversity and (teacher) education, two in-service teacher educa- tors specialized in teacher professional development for diversity, and two teachers. Through this process, the questionnaire ended up consisting of 128 items, which were then presented in the first step of the research to a large-scale group of pre-service teachers. The questionnaire was administered in Dutch, the official language of Flanders. The questionnaire. The questionnaire consists of two parts. Part one considers teachers’ beliefs by answering on a 7-point Likert scale (0 = completely disagree, 6 = completely agree) to allow for nuanced answers, in line with psychometric recommendations for Likert-scales [49]. Furthermore, given that inclusive teaching has become an obligatory professional competence, and hence a norm in education, this increased the chance of social desirability bias and ceiling effects in respondents’ answers [50]. To counteract this, we provided respondents with a large

range of items that were critical of inclusion or student diversity, and hence, were reverse-coded. The first component taps teachers’ professional beliefs on diversity, specifically with regards to students with ethnic minority background (e.g., “The more immigrant students in a school, the more discipline problems the school will face”), with a disability (e.g., “Students with a disability reduce the learning opportunities for the other students in the class”), from lower socio-economic backgrounds (e.g., “underprivileged parents are often less interested in their children’s progress in school than other parents”), with regards to essentialist notions on the gender binary (e.g., “I think it’s good that girls are not asked to help out with jobs in school that involve heavy lifting”), and LGB-students (e.g., “many students experiment with their sexuality just to get noticed”). The second component consists of responsibility-beliefs, and is divided in two sections. The first one taps the extent to which teachers believe it is the responsibility of the educational field to create maximal developmental opportunities for diverse students. These 33 items con- sider general items (e.g., “Teachers have a didactical task in the classroom, not one of raising students or caring for them.”) as well as with regards to specific groups of students (e.g., “The school must allow students with a migration background to speak a language other than Dutch at school”, “it is time to pay attention to LGB-sexuality in several parts of the curriculum”).

The second section taps teachers’ perceptions of to what extent they should collaborate with both diverse parents and colleagues. These 16 items are preceded by the stem “It is my job to. . .” followed by, for instance, “Establish a good relationship with all parents, even if I do not like them” or “learn from colleagues with a completely different teaching approach”. The second part of the questionnaire contains 42 items considering self-efficacy, consisting of three dimensions. In line with other validated efficacy scales [51,52], these items are pre- ceded by the stem “To what extent are you able to. . .” and is answered on a 9-point Likert scale (0 = not at all, 8 = a lot). The first dimension contains 9 items tapping teachers’ percep- tions of being able to notice student diversity (f.i., students’ background, interests, well-being, . . .) with, for instance, “make time for in-depth individual conversations with all of your stu- dents in order to provide more effective support”. The second dimension taps the extent to which teachers feel capable to design a classroom environment that takes into account the needs of their students and contains 21 items (e.g., “Give students opportunities beyond tradi- tional tests and exams to demonstrate their knowledge and skills”). The third dimension mea- sures the extent to which teachers feel capable to create positive interactions among students through 12 items (e.g., “Coach students to treat other opinions with respect.”). PLOS ONE Measuring teachers’ competences for inclusive education

PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 6 / 22

Plan of analysis. To validate the factor structure underlying the DISCO-instrument, we combined exploratory (EFA) and confirmatory factor analyses (CFA) in a stepwise approach. In order to maximize power for the analyses and following the full information maximum like- lihood (FIML) on missing data theory [53], all available data was used for the factor analyses. Hence, respondents were not a priori list-wise deleted from the dataset for having missings on some survey-items. In the first step, using the data from pre-service teachers, exploratory fac- tor analysis using SPSS 25 was chosen to identify a (set of) latent constructs underlying the measured items without strong theoretical assumptions on how many factors existed [54]. Because teachers’ competences in handling diversity were expected to correlate [54,55], Princi- pal Component Analysis (PCA) with oblique rotation technique (direct oblimin) was used. The assumptions to perform EFA were checked: data distributions were checked to ensure that variables were roughly normally distributed [54] and the correlation-matrix was inspected to identify scale items that correlated below |.30| with all other variables or above |.80|. The suitability of the data for the exploratory analysis were checked by considering the Kaiser– Meyer–Olkin test (KMO) which should exceed the recommended value of .60, and the Bart- lett’s test of sphericity which should be significant. Furthermore, the anti-image correlation matrix was checked for negative correlations, low communalities or high partial correlations

[54]. To determine the number of factors, both the scree plots’ point of inflexion and Kaiser’s criterion (eigenvalue >1) were checked [54]. Items were eliminated if they had inadequate (partial) correlations or high cross-loadings (>|.40|), if their variance was not well explained as suggested by low communalities, or if the loading on their designated factor was weak (<|.35|). When a choice for being dropped or retained had to be made between items, the the- oretical interpretability and alignment with EfA tenets spurred the decision besides psycho- metric considerations. Factors with a minimum of three items and Cronbach’s alpha >.70 were retained for testing in the second step [54]. For the second step, the survey was adapted according to the insights from the first step and then presented to a new sample consisting of in-service teachers. The initial factor solution from step 1 was checked with data from these in-service teachers using confirmatory factor analyses in Mplus. This technique allows us to check to what extent a hypothesized model fits the data. An MLR estimation was used, and goodness of fit indicators were checked: CFI values larger than 0.95, X2/DF smaller than two, RMSEA values smaller than 0.05 and SRMR values smaller than 0.05 are considered good [56]. Where necessary, the model was optimized based on suggestions of the modification indices, standardized factor loadings, R-square estimates of the items, and theoretical interpretability of the factor. To compare models, we checked which

model had a lower AIC value. Note that X2 statistics are reported to increase transparency for the X2/DF calculation, but that the X2 statistics themselves are not discussed because the test is sensitive to large sample sizes [57]. Finally, based on these results, the scale scores for in-service teachers were obtained by computing a mean for each respondent with a maximum of 25% missing values on the scale- items. The final set of items for each scale can be seen in Tables 2 and 3. Repeated measures analysis of variance with a bonferroni post-hoc test was conducted to examine possible signifi- cant differences on scale scores for efficacy and beliefs. Results Step 1: EFA with pre-service teachers Professional beliefs about diverse students. Based on the data distributions, correlation matrix and anti-image correlation matrix, ten items were deleted (see Table 1). PCA on the remaining 27 items revealed satisfactory KMO-value, anti-image correlations and Bartletts’ PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 7 / 22

Table 1. Overview of decisions on all scale-items and factors throughout the analyses (Note that items relating to the factor “broad role of teachers” are indicated in grey for recognazibility). original scale-name Item Nr To what extent are you able to. . .? / Do you agree with . . .? Decision after step 1 Reason for decision Decision after step 2 Reason for decision Final scale-name Self-efficacy in Noticing diversity C1.01 Talk to colleagues to evaluate or adjust your image of a student delete low communality score Noticing diversity Self-efficacy in C1.02 Make time for in-depth individual conversations with all of your students in order to provide more effective support. C1.03 Gain insight into the learning needs of an individual student by consciously looking at how he/she responds to different tasks and works in different groupings. C1.04 Gain insight into a student’s skills and learning tempo by checking their independent work while they are working on it. delete high partial correlations with C1.03 C1.05 Gain insight into a student’s plans and dreams for the future. C1.06 Start a conversation with a student who is not attentive or is having a difficult time outside of the classroom. C1.07 Gain insight into social relationships among students. C1.08 Get a complete picture of a student during the first lessons (to a class group). delete negative correlations with all other items C1.09 Gain insight into the students’ feelings about their family situation. High-quality student- interactions

C3.01 Have students work together in heterogeneous groups. delete low communality score High-quality student- interactions C3.02 Rrespond to racist statements by students. delete skewed distribution / ceiling effect C3.03 Allow students with learning difficulties to be helped by other pupils. C3.04 Coach students to treat other opinions with respect. delete skewed distribution / ceiling effect C3.05 Give tasks where the students have to work together to complete the task successfully (for example, each having a different role). C3.06 Provide feedback on how students work together. C3.07 Create space in or outside the classroom to support students in the resolution of conflicts. C3.08 Respond to homophobic statements made by students. delete skewed distribution / ceiling effect C3.09 Coach students to give each other thorough and respectful feedback. delete suggested by modification indices C3.10 In group work, ensure that all pupils get to work with others from all across the class? C3.11 draw up clear rules for the classroom together with the pupils. delete suggested by modification indices C3.12 In the case of bullying, discuss a plan of action with the students involved. Creating stimulating learning environment C4.01 Ensure that teaching materials reflect diversity in society. Creating stimulating learning environment C4.02 Break stereotypes. delete high partial correlations with C4.01 C4.03 Address sensitive themes, such as discrimination, radicalization, gaybashing, cat-calling,. . . delete inadequate score on anti-image correlation

C4.04 Use a wide range of evaluation methods in order to evaluate students in a broad a way as possible. C4.05 Take into account how much progress students have made when I evaluate them. delete high partial correlations with C4.04 C4.06 Specifically check that students with a language delay have understood a question. C4.07 Enter into dialogue with students about their results. C4.08 Occasionally use a short moment of evaluation (e.g., quiz) to tailor your lesson in a more nuanced way to the students’ needs. C4.09 take the linguistic background of students into account during evaluation moments (e.g. by not counting language errors). delete low communality score C4.10 Give students opportunities beyond traditional tests and exams to demonstrate their knowledge and skills (e.g. through portfolios, writing tasks, oral presentations). C4.11 Allow students to give input about content that they would like to cover in lessons. C4.12 Have students evaluate your lessons. C4.13 When managing the pace of your lessons, take account of students who work faster/slower than the others. C4.14 Offer a variety of activities so that students can choose what to do themselves. C4.15 Provide a wide variety of assignments, according to the needs and skill level of students. delete high partial correlations with C4.14 C4.16 Allow students to choose whether or not to use certain tools/support. C4.17 Present content in different ways (eg text, audio material, visual material). delete high partial correlations with C4.18

C4.18 Use a variety of teaching materials and media which invite pupils to draw on different senses. C4.19 When necessary, adapt your learning objectives (knowledge and skills) to take account of differences between students (e.g., by creating main and advanced learning goals). C4.20 Allow all students to ’show off’ sufficiently with what they are good at, including their extracurricular skills. delete inadequate score on anti-image correlation C4.21 Let all students ’show off’ sufficiently with what they have done during an exercise, homework, class assignment, role play. delete high partial correlations with C4.20 (Continued) PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 8 / 22

Table 1. (Continued) original scale-name Item Nr To what extent are you able to. . .? / Do you agree with . . .? Decision after step 1 Reason for decision Decision after step 2 Reason for decision Final scale-name Beliefs on the responsability of the educational field to create EfA, focused on collaborating with parents & colleagues C5.01 Make parents from different backgrounds feel comfortable about coming into school. stem changed from "it is my job to. . ." to "To what extent are you able to. . .?" skewed distribution / ceiling effect collaborating with parents C5.02 Help parents to support their children to do well in school. C5.03 Involve the parents of students with special needs in their children’s educational career. C5.04 Adapt the way you communicate with different kinds of families (e.g. single parents, LGBT+ parents, non- native speakers. . .). C5.05 Empathize with the situation and motivations of different parents. delete suggested by modification indices C5.06 Use the insights that parents give you about their child. C5.07 Establish a good relationship with all parents, even if you do not like them. C5.08 Actively make time for parents who want to have a conversation with me. delete suggested by modification indices C5.14 Always be available for questions from parents during school hours. C5.15 Allow parents to give some input about my lessons. C5.09 Consult other professionals (e.g.: SEN teachers, speech therapists, . . .) when one of your students has extra needs. delete suggested by theoretical interpretability, r-square

values and factor loadings collaborating with colleagues C5.10 Involve the school team (e.g.: teachers, student counselor, . . .) when one of your students has extra needs. delete suggested by modification indices, r-square values and factor loading C5.11 Integrate lesson ideas from colleagues into your own teaching practice. C5.12 Ask colleagues for feedback to improve your teaching. C5.13 Create new teaching methods or materials together with colleagues in order to support students with learning difficulties. C5.16 Share learning materials with colleagues that meet students’ different learning profiles. delete suggested by r-square values and factor loadings Ethnic minorities C6.01 The school should provide specific services for students who want to follow religious practices (e.g., prayer room, halal/kosher food). Ethnic minorities Beliefs on the responsability of the educational field to create EfA, focused on C6.02 The school must allow students with a migration background to speak a language other than Dutch at school. C6.03 As a school, you should not take into account the fatigue of Muslim students participating in Ramadan. delete low correlations with other items C6.04 The school library should have books in the different home languages of the students. C6.05 It is important to encourage students of immigrant origin to be proud of their ethnic and cultural background. C6.06 As a teacher, it is your job to react to racist statements by students. delete low correlations with other items

Disability C6.07 It is time that we give children with a disability a full place in mainstream education. It is their right. Disability C6.08 It is sensible to not send students to special educational support too quickly. C6.09 The school’s infrastructure must be made accessible at all levels to people with physical and sensory disabilities (vision, hearing, motor). C6.10 You cannot expect the teacher to meet the needs of a child with a disability in mainstream education. C6.11 It is normal to prepare extra tasks for students who work at a higher or lower level. delete low correlations with other items SES C6.12 The influence of a teacher is limited compared to the influence of the pupil’s home environment. delete part of scale with low cronbach’s alpha General policy C6.13 Teachers must be capable of working with students from different home situations. C6.14 Students from families with financial problems should be provided with appropriate support (e.g. payment plan, special support fund for students who cannot pay the school fees). C6.15 A school cannot be held responsible if underprivileged pupils benefit little from the education offered. delete low correlations with other items C6.16 A teacher can make a difference for students from all kinds of home environment. Gender binary C6.17 You cannot expect a school to change the toilet infrastructure for a single transgender student. delete low correlations with other items C6.18 Students sending sexually suggestive photos to each other is beyond the responsibility of the school. delete low correlations with

other items C6.19 Making students aware of inequality between men and women is outdated. delete low correlations with other items C6.20 It is important that we as a school respond quickly and consistently to incidents of sexual harassment among students. delete skewed distribution / ceiling effect C6.21 As a school, it is important to break the traditional divide between subjects that are stereotypically for boys or for girls. LGB C6.22 As a teacher, it is your job to respond to homophobic statements by students. delete suggested by r-square values and factor loading C6.23 It is too cumbersome to adapt all school communication (f.i. the salutation in a letter) to LGB parents. delete low correlations with other items C6.24 It is time that we have attention for LGB sexuality in various parts of the curriculum. delete high partial correlations with C6.25 C6.25 It is our job as a school to support students coming out of the closet during this process. delete low communality score C6.26 As a school, It is normal to support LGB colleagues through thick and thin, even in the event of negative reactions from the school community. delete skewed distribution / ceiling effect A general approach C6.27 It is the responsibility of every teacher to support the language development of pupils delete skewed distribution / ceiling effect C6.28 Teachers have a didactical task in the classroom, not one of raising students or caring for them. delete part of scale with low cronbach’s alpha

C6.29 It is important that your work contributes to the personal growth of students. delete suggested by modification indices and low factor loading C6.30 For a teacher, professional knowledge is more important than knowledge of didactics and psychology. delete part of scale with low cronbach’s alpha C6.31 The future of the current generation of students often concerns me delete low communality score C6.32 I think it is important to mean something personally to students. delete high partial correlations with C6.29 C6.33 A teacher is not a youth or social worker. delete part of scale with low cronbach’s alpha C6.43 A school has the task of combating inequality in society new item added delete suggested by modification indices C6.44 It is every teacher’s job to contribute to a school policy that is mindful of diversity. new item added (Continued) PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 9 / 22

test. The scree plot and Kaiser criterion indicated that it was reasonable to retain four factors. Inspection of the rotated solution revealed an item loading below .3 unto its designated factor, which was deleted. The PCA on the remaining 26 items similarly revealed that it was reason- able to retain four factors. Communalities ranged from .32 to .60. These four factors explained 46.48% of the total variance and had eigenvalues of 25.81, 9.83, 6.13, and 4.71 respectively. To interpret these factors, we made use of an oblimin rotation. The factor correlation matrix indeed shows that there was a moderate correlation between the various factors (r-values between |.152| and |.363|). The first factor consisted of 6 items tapping beliefs towards ethnic minority students, with factor loadings ranging from .38 to .77, and a Cronbach’s alpha of .77. The second factor consisted of 9 items tapping beliefs on sexual orientation and essentialist notions on the gender binary, with factor loadings ranging from .51 to .69, and a Cronbach’s alpha of .82. The third factor consisted of 6 items tapping beliefs towards students with a Table 1. (Continued) original scale-name Item Nr To what extent are you able to. . .? / Do you agree with . . .? Decision after step 1 Reason for decision Decision after step 2 Reason for decision Final scale-name professional beliefs on student diversity Ethnic minorities C2.01 Ethnic and cultural diversity is a valuable resource in education. Ethnic minorities professional beliefs on student diversity

C2.02 Immigrant parents are less involved in their child’s school career. delete factor-loading <0.3 C2.03 If there are more “native-born” pupils in a school, it means that academic achievement will be higher across the board. C2.04 If an additional language is spoken at home, the student will fall behind in their learning. C2.05 Schools that educate many migrant students have lower standards. delete high partial correlations with C2.35 C2.06 Immigrant students are not as good at mathematics as native students. C2.07 Students who speak a different language at home will never speak Dutch properly. C2.08 The more immigrant students in a school, the more discipline problems the school will face. LGB C2.09 It doesn’t matter to me if my principal has a same-sex partner. delete skewed distribution / ceiling effect essentialist notions on the gender binary & sexual orientation C2.10 It is better for partners of LGBs not to come to school parties and other school activities. delete skewed distribution / ceiling effect C2.11 Many students experiment with their sexuality just to get noticed. C2.12 LGB students who behave in an exaggerated manner are asking to be bullied. delete suggested by modification indices C2.13 LGB teachers have the right to be open with students about their sexual orientation. delete multicollinearity with C2.14 C2.14 LGB teachers (lesbian, gay, bisexual) have the right to be open with parents about their sexual orientation. C2.15 In order for their time in school to go smoothly, it is better for LGBT students not to openly display their

sexual orientation. C2.16 I feel sorry for students who grow up in an LGBT family because it is not easy for them. Gender binary C2.25 Boys shouldn’t wear earrings or nail varnish when in school. C2.26 It is no problem at all that girls opt for ’soft’ study options/professions (e.g. languages, care) and boys for ’hard’ study options/professions (e.g. sciences, technology). delete low correlations with other items C2.27 Two boys should be able to dance together for the entire evening at the school dance without attracting undue attention. C2.28 I find it difficult to understand transgender students. C2.29 I think it’s good that girls are not asked to help out with jobs in school that involve heavy lifting. C2.30 Girls will generally work more neatly and punctually than boys. delete low correlations with other items C2.31 In a class with many boys, classroom management is often more difficult. delete low correlations with other items Disability C2.17 The care for pupils with a disability is worthwhile, but is often at the expense of attention for other pupils. delete suggested by modification indices, r-square values and factor loading Disability C2.18 I find it difficult to like students with behavioral disorders as much as other students. delete suggested by r-square values and factor loading C2.19 I find it difficult to teach students with a learning disability. delete high partial correlations with C2.18 C2.20 Students with a disability always score worse on tests than other students.

C2.21 Students with a disability reduce the learning opportunities for the other students in the class. C2.22 Students with a disability often abuse the support that they receive. C2.23 It is fair that a stronger student is given a more difficult test. delete low correlations with other items C2.24 I think that many teachers show too much understanding for the behaviour of students with a disability. SES C2.32 How many abilities a pupil has is independent of the home environment. delete low correlations with other items SES C2.33 Underprivileged parents are often less interested in their children’s progress in school than other parents. C2.34 It is difficult to be sympathetic towards poorer students if they or their parents always have the latest mobile phones or gadgets. C2.35 Schools that educate many underprivileged students have lower standards. C2.36 Underprivileged students rarely succeed in difficult subjects because they do not have supportive parents. C2.37 It is acceptable for teachers to have higher expectations of students from well-off backgrounds. https://doi.org/10.1371/journal.pone.0291033.t001 PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 10 / 22

disability, with factor loadings ranging from .57 to .72, and a Cronbach’s alpha of .77. The final factor consisted of 5 items tapping beliefs towards low SES-students, with factor loadings rang- ing from .42 to .72, and a Cronbach’s alpha of .72. Responsibility of the educational field to create Education for All. Based on the data distributions, correlation matrix, and anti-image correlation matrix, fifteen items were deleted (see Table 1). PCA on the remaining 18 items revealed satisfactory KMO-value, anti-image correlations and Bartletts’ test, and that it was reasonable to retain four factors. Communalities ranged from .41 to .72. These four factors explained 53.98% of the total variance and had eigenvalues of 25.42, 11.55, 9.04, and 7.97 respectively. The factor correlation matrix shows that there was a correlation between the various factors (r-values between |.134| and |.281|). Interestingly, the revealed factors did not line up directly with the diversity groups included in the items. Rather, the first factor, consisting of 6 items, seemed to tap a broad sense of school responsibility, including general items and items with regards to tackling discrimination based on SES, gender and sexuality. This factor had loadings ranging from .62 to .75, and a Cron- bach’s alpha of .71. The second factor tapped beliefs on school approaches specifically directed at ethnic minority students, consisting of 4 items with loadings ranging from .45 to .86, and a Cronbach’s alpha of .70. The third factor consisted of 4 items representing beliefs on the broad

service teachers were presented with 16 items preceded by the stem “To what extent are you able to. . .” and a 9-point Likert scale (0 = not at all, 8 = a lot). Self-efficacy in noticing student diversity. The 9 items had a KMO value of .902 and Bartletts’ test was significant (X2 = 4584, df = 36, p < .001). Inspecting the anti-image correla- tion matrix led to the deletion of three items (see Table 1). PCA on the remaining 6 items revealed satisfactory KMO-value, anti-image correlations and Bartletts’ test. The scree plot and Kaiser criterion indicated one factor to extract with an eigenvalue 4.00, which explained 67% of the total variance. Factor loadings ranged from .76 to .84, and communalities ranged from .58 to .72. The scale had high internal reliability (α = .90). Self-efficacy in creating stimulating learning environments for diverse students. Inspection of the correlation matrix and anti-image correlation matrix revealed several prob- lematic item-sets, so eight items were deleted (see Table 1). PCA on the remaining 13 items revealed satisfactory KMO-value, anti-image correlations and Bartletts’ test. The scree plot and Kaiser criterion indicated one factor to extract with an eigenvalue 7.43, which explained 57.2% PLOS ONE Measuring teachers’ competences for inclusive education PLOS ONE | https://doi.org/10.1371/journal.pone.0291033 November 8, 2023 11 / 22