Longitudinal data from an at-risk sample were used to analyze individual linear trend scores for each of three new forms of problem behavior that emerges during the interval from age 10 through 18 years. Growth in substance use, health-risking sexual behavior and police arrests defined a latent construct for growth in adolescent problem behavior. A structural equation model (SEM) showed a significant path from early involvement with deviant peers to a latent construct for growth in new forms of antisocial behavior. A second SEM showed that the contribution of early involvement to later growth was mediated by a latent construct for deviancy training assessed at age 14 years. The relative rates of reinforcement for deviancy, amount of time spent with deviant peers, and deviancy level of the peer network defined a deviancy training construct that accounted for 53% of the variance in later growth in new forms.