The nationally representative sample of 15-year-old students investigated in the PISA study (Programme for International Student Assessment) provides achievement data for reading and mathematics. Together with available data on verbal and math self-concept, the PISA study allows central models on determinants of academic self-concepts to be tested. We thus analyzed data of N = 4861 students from 203 schools to test the Internal/External Frame of Reference Model (I/E Model; Marsh, 1986) and the Big-Fish-Little-Pond Effect (BFLPE; Marsh, 1987). Multilevel analyses show that, in line with the I/E Model, achievement indicators have positive effects on academic self-concepts in the same domain, but negative effects on academic self-concepts in the other domain. Furthermore, the BFLPE is replicated, that is, the higher the school-average math achievement, for example, the lower the math self-concept. Even after controlling for grades, the BFLPE remains significant. Educational implications of the findings are discussed.