This study examines the role of racial/ethnic segregation and peer effects in shaping educational achievement and attainment, using multi-level modeling on a nationally representative sample of adolescents. As in many prior studies, school socioeconomic composition was a significant predictor of achievement and attainment for students of all racial/ethnic groups. Educational attainment was negatively affected by the concentration of low-income students. However, for some racial/ethnic groups educational attainment increased with higher concentrations of minority students. Furthermore, peer social capital, measured as the average achievement of a peer network, was a significant predictor of both educational achievement and attainment for all racial/ethnic groups. In addition, and counter to some earlier studies, results revealed that segregated peer networks among African-Americans may lead to better academic achievement and attainment than school settings with more integrated friendship networks. (Contains 4 tables.)