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

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