The influence of the ethnic composition of schools on interethnic relations and attitudes has been studied extensively and has received ample interest from policy makers. However, less attention has been paid to the structures and processes inside schools that organize interethnic relations and attitudes. In Flanders (Belgium), secondary education is organized by grouping students in different tracks, which are hierarchically ordered and prepare students for different futures. Tracking in Flanders is intended to group students according to their abilities but together with this, students are grouped according to their ethnic and socioeconomic background. In the present study, the interethnic relations and attitudes in each track will be explored, based on ethnographic observations and semi-structured interviews in three multi-ethnic secondary schools in one city. Our findings suggest that different patterns occur across three groups of tracks: the most appreciated fields of study in academic, the intermediary (less appreciated fields of study in academic and technical tracks) and vocational tracks. According to the relative sizes of ethnic groups and track specific characteristics, interethnic relations were characterized respectively by ethnic segregation, positive experiences of interethnic contact or ethnic conflict/tensions. The ethnic composition of classrooms seemed to matter for students' ethnic in-group identifications and evaluations and perceived out-group threats.