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It has been long known that human relationships are genetically stratified. Whether genetic similarity among those in a relationship is due to complex ancestral patterns linked to historical migration, macro-level social structures in modern society, or individual-level peer selection remains unsettled. We use data from 9,500 adolescents from the the National Longitudinal Study of Adolescent to Adult Health to examine genetic similarity among school-based friends. While friends have correlated genotypes, both at the whole-genome level as well as at trait-associated loci (via polygenic scores), the results suggest that macro-level forces, such as school assignment, are a prime source of genetic similarity between friends. Further, we find evidence consistent with the existence of social genetic effects as an individual's educational attainment is strongly associated with the polygenic scores of those in their broader social environment (e.g., school) and of their friends (net of their own score). In contrast, individual BMI and height are largely unassociated with the genetics of peers.