Starting from a person–environment fit framework, this study investigates whether ethnic congruence—the percentage of co-ethnics in a school—relates to school misconduct and whether congruence effects differ between ethnic minority and majority students. Moreover, we investigate whether eventual associations are mediated by friendship attachment, perceived teacher support, and general school belonging. Multilevel analyses of data from 11,759 students across 83 Flemish secondary schools show that higher ethnic congruence is associated with lower levels of school misconduct but only for ethnic minority students. This effect was not mediated by friendship attachment, nor by teacher support, but it was mediated by general school belonging. We conclude that ethnic minority students in schools with a higher percentage of peers of co-ethnic descent are less likely to break the school rules because they feel more contented in the school context, which is congruent with the person–environment fit framework.