Teacher-student-relationship quality is associated with academic success and, among ethnic minority adolescents, it can promote positive intergroup relations. However, most research has studied student or teacher reports only and rarely accounted for ethnic classroom heterogeneity. This study investigated teacher-student-agreement on relationship quality in minority and majority student-teacher-dyads and tested predictors of relationship quality in adolescence. The sample comprised 309 minority (Mage = 12.99, SD = 1.30) and 200 majority adolescents (Mage = 13.50, SD = 1.56) and their 28 majority teachers (Mage = 45.82, SD = 11.50). Teachers reported higher relationship quality than students. Correlations in student-teacher-dyads were similar for minority and majority students. A better school climate, teachers’ awareness of social heterogeneity and culturally responsive teaching predicted relationship quality in student reports, whereas teaching enjoyment predicted relationship quality in teacher reports. In minority dyads, higher student socioeconomic status (SES) and lower levels of discrimination were additional predictors for relationship quality in both student and teacher reports. Findings suggest different processes in how minority and majority student-teacher-dyads evaluate relationship quality.