The consequences of teaching in schools with a high degree of ethnic minority students are rather unknown. Anglo-Saxon findings suggest a lower job satisfaction of the teachers in schools with more ethnic minority students. Research in Flanders is, however, nonexistent. This research examines (1) whether the job satisfaction of teachers varies with the ethnic school composition in Flanders, and (2) what part the expectations for the students, the perceived relationship quality, and the teacher efficacy play in this variation. Multilevel analyses of data from 2104 teachers in 84 secondary schools show that in Flanders, it is the socioeconomic school composition rather than the ethnic school composition which is important for the job satisfaction of teachers. The lower the socio-economic composition, the lower the expectations for the students. This undermines the job satisfaction, both directly and indirectly, through a lower perceived relationship quality and a lower teacher efficacy.