The multi-decade growth and spatial dispersion of immigrant families in the United States has shifted the composition of US schools, reshaping the group of peers with whom students age through adolescence. US-born students are more likely to have foreign-born peers and foreign-born students are more likely to be educated outside of enclaves. This study examines the short-term and long-term impact of being educated with immigrant peers, for both US-born and foreign-born students. We leverage a quasi-experimental research design that uses across-grade, within-school variation in cohort composition for students in the Add Health study. We describe effects on a broad set of education, social, and health outcomes. For US-born students, we find little evidence that having immigrant peers affects a wide array of outcomes, either in adolescence or in adulthood. For foreign-born students, attending school with other immigrant students is protective against risky health behaviors and social isolation, relative to native born students. However, foreign-born students’ language skills measured with Picture-Vocabulary Test scores are negatively affected by attending school with a larger share of other immigrant students. The negative effect on vocabulary scores persists through young adulthood but does not translate into reductions in most longer-run socioeconomic outcomes, including earnings or the economic status of their residential neighborhoods.