Using data on primary school children and their teachers, we show that teachers who hold prejudicial attitudes towards an ethnic group create socially and spatially segregated classrooms. Leveraging a natural experiment where newly arrived refugee children are randomly assigned to teachers within schools, we find that teachers' ethnic prejudice, measured by an implicit association test, significantly lowers the prevalence of interethnic social links, increases homophilic ties among host children, and puts refugee children at a higher risk of peer violence. Our results highlight the role of teachers in achieving integrated schools in a world of increasing ethnic diversity.

We study the effect of elementary school teachers’ beliefs about gender roles on student achievement. We exploit a natural experiment where teachers are prevented from self-selecting into schools, and, conditional on school, students are allocated to teachers randomly. We show that girls who are taught for longer than a year by teachers with traditional gender views have lower performance in objective math and verbal tests, and this effect is amplified with longer exposure to the same teacher. We find no effect on boys. We show that the effect is partly mediated by teachers’ transmitting traditional beliefs to girls.