This article argues that the Czech education system is structured to operate in an ethnically homogeneous society. Although the Czech Republic is becoming increasingly heterogeneous, teachers deploy discursive practices of "sameness despite difference" that obscure such growing diversity. This article is grounded in the historical context of migration to and from the Czech Republic and based on ethnographic research in several ethnically-mixed classrooms. We analyze the ways in which teachers talk about their pupils. We show that in the case of migrant children, teachers tend not to see their differences and hence, their potentially structural disadvantages. On the other hand, the Roma ethnicity is perceived as insurmountable. Teachers mobilize lists of cultural and even genetic differences to legitimize their different treatment of Roma pupils. Furthermore, we analyze policy documents regarding the education of non-Czech pupils and their reception by teachers. All these strategies result in the continuing perception of Czech classrooms as ethnically homogeneous while disregarding any social inequalities.