OBJECTIVES: We examined the extent to which within-school segregation, as measured by unevenness in the distribution of Black and White adolescents across levels of the English curriculum (advanced placement-international baccalaureate-honors, general, remedial, or no English), was associated with smoking, drinking, and educational aspirations, which previous studies found are related to school racial/ethnic composition. METHODS: We analyzed data from wave 1 of the National Longitudinal Study of Adolescent Health, restricting our sample to non-Hispanic Blacks (n = 2731) and Whites (n = 4158) who from 1994 to 1995 attended high schools that enrolled Black and White students. RESULTS: White female students had higher predicted probabilities of smoking or drinking than did Black female students; the largest differences were in schools with high levels of within-school segregation. Black male students had higher predicted probabilities of high educational aspirations than did White male students in schools with low levels of within-school segregation; this association was attenuated for Black males attending schools with moderate or high levels of within-school segregation. CONCLUSIONS: Our results provide evidence that within-school segregation may influence both students' aspirations and their behaviors. [ABSTRACT FROM AUTHOR]