A social learning model which incorporates measures from both the sociological perspective of differential association and the psychological perspective of behavior reinforcement is analyzed as an explanation of continued alcohol and marijuana use among youths. Data were gathered at two points in time from a sample of adolescents from New Jersey. The measurement and structural relationships among peer associations, attitudes, reinforcing and punishing consequences, and patterns of use were examined. It was found that, overall, the model fit the data for use of both substances, proving to be invariant across age and gender groups. The most pronounced difference between the alcohol and marijuana models was that differential associations exhibited the strongest relationship to maintenance of alcohol use while reinforcers were most salient to continued marijuana use.