Determinants of the use of alcohol, alcohol without parental knowledge, cigarettes, marijuana, and crack were assessed in predominantly black, urban, fourth- and fifth-grade students. Each subject identified three best friends. Logistic and least-square regression analyses indicated that children's perceptions of friends' use, perceptions of family use, and actual use of classmates were better predictors of substance use than friends' actual use. The pattern of predictors suggested that peer behaviors and attitudes are more influential for children's socially censured behaviors such as using alcohol without parental permission than for more socially approved behaviors such as using alcohol with parental permission. The importance of perceived friends' use vs. friends' actual use supports Behavioral Intention Theory and Cognitive Developmental Theory, while the importance of classroom use supports Social Learning Theory or may reflect social and environmental conditions including neighborhood availability of drugs and neighborhood values regarding substance use.