From the Second World War onwards, Belgium became a migration society and, over the past few decades, Flanders -the northern, Dutch-speaking part of Belgium- has rapidly developed into a multi-ethnic society, making Flemish schools much more ethnically diverse. This study contributes to the existing research by examining the association between ethnic school composition and teachers’ ethnic prejudice, controlling for individual characteristics of teachers and taking into account teachers’ perceptions of pupils’ teachability. Multilevel analyses of data, including 499 ethnic majority teachers in 44 Flemish secondary schools, show that the effect of ethnic school composition is suppressed by teachers’ perception of ethnic minority pupils as less teachable in schools with a higher proportion of ethnic minority pupils. Hence, a higher proportion of ethnic minority pupils in school is associated with less Flemish teachers’ ethnic prejudice more when teachers evaluate their pupils as teachable. The implications of these findings are discussed.