The authors examine whether school segregation is related to pupils' global self-esteem and whether this association is mediated by teacher-pupil relationships. Multilevel analyses based on a survey of 2,845 pupils (aged 10 to 12) in 68 primary schools in Belgian urban areas reveal that, for native-Belgian pupils, a higher proportion of immigrants at school is associated with increasing self-esteem. Initially no such association was found for immigrant pupils, as the effect of schools' ethnic composition on their self-esteem was suppressed by teacher-pupil relationships. For both groups, experiences of supportive relationships with teachers were largely associated with self-esteem. (Contains 5 tables.)