Examined data from the National Longitudinal Study of Adolescent Health to determine impact of school-level substance use on adolescent-peer similarity for smoking and drinking. Found that adolescent-peer similarity was significantly moderated by school-level substance use for both tobacco and alcohol use. Inferred that schools with relatively few substance-using peers provide fewer opportunities for adolescents to pick niches that expose them to risk factors corresponding to their own substance-use behaviors. (Author/KB)