In a large nationally representative sample (N = 14,825 students, 1,015 high schools) math and English self-concepts were: (a) uncorrelated despite a substantial correlation between math and English test scores; (b) influenced by internal and external frames of reference; and (c) negatively affected by school-average achievement. As posited by the internal/external frame-of-reference model, better math skills led to much higher math self-concepts but slightly lower English self-concepts, whereas better English skills led to much higher English self-concepts but slightly lower math self-concepts. School-average achievement negatively affected academic self-concept; equally able students had higher academic self-concepts in schools with lower school-average achievements. This school context effect was also content specific; school-average math achievement negatively affected only math self-concept, and school-average English achievement negatively affected only English self-concept. © 1990 American Psychological Association.