This 4-year study of 698 young adolescents examined the covariates of early onset substance use from Grade 6 through Grade 9. The youth were randomly assigned to a family-centered Adolescent Transitions Program (ATP) condition. Variable-centered (zero-inflated Poisson growth model) and person-centered (latent growth mixture model) approaches were taken to examine treatment effects on patterns of substance-use development across early adolescence. Variable-centered analyses revealed treatment effects both on decreasing the likelihood of initiating substance use and on the rate of growth in substance use among those who initiated use. Person-centered analyses revealed the following five trajectories of early substance use: (l) no use, (2) low/rare use, (3) early accelerating use, (4) late-accelerating use, and (5) early high but decreasing use. Of note, random assignment to the ATP intervention was strongly predictive of following the decreasing-use trajectory. In addition, the early high but decreasing group was most likely to engage in the Family Check-Up and linked intervention services. These findings suggest that covariates of early adolescent substance use, as well as the effectiveness of prevention strategies, vary as a function of the developmental pattern underlying early adolescent risk.