This research examines the effects of school racial and ethnic composition on students' academic achievement in the U.S. using the National Longitudinal Study of Adolescent Health and hierarchical linear models. This analysis includes Hispanics, which stands apart from other research in this area that has traditionally focused on only Black and White student racial composition. In addition, peer group influences are measured by utilizing the comprehensive peer network data available for all respondents in the sample. Interactions between individual race/ethnicity and school racial/ethnic composition are also tested to better understand the possible differential effects of racial/ethnic composition for each race/ethnicity. The results show that school and peer racial/ethnic composition has important effects on individual level achievement. (Contains 3 tables.)