Data of N = 1939 students from German upper secondary schools ("Gymnasien") were analyzed to test the big-fish little-pond-effect (BFLPE; Marsh, 1986, 1990). All students participated in the Third international Mathematics and Science Si;hy (TIMSS). The;BFLPE describes the phenomenon that attending classes or schools where, for example, class-average math achievement, is higher, typically leads to lower math self-concepts after controlling for individual achievement. In the current study, individual and school-average mathematics achievement as well as course work selection (basic vs, advanced math course) served as predictors, while domain-specific self-concept and interest in mathematics were dependent variables. Based upon hierarchical linear modeling (Bryk & Raudenbush, 1992) the BFLPE was replicated for self-concept and was also reliable for interest. Furthermore, course work selection affected self-concept and interest, i.e, students: of advanced math courses scored higher on both dependent variables. Instructional implications are to be discussed.