This study examines the effects of 2 brief family-focused interventions on the trajectories of substance initiation over a period of 6 years following a baseline assessment. The 2 interventions, designed for general-population families of adolescents, were the 7-session Iowa Strengthening Families Program (ISFP) (Molgaard & Spoth, 2001) and the 5-session Preparing for the Drug Free Years Program (PDFY) (Catalano, Kosterman, Haggerty, Hawkins, & Spoth, 1999). Thirty-three rural public schools were randomly assigned to the ISFP, the PDFY, or a minimal-contact control condition. The authors evaluated the curvilinear growth observed in school-level measures of initiation using a logistic growth curve analysis. Alcohol and tobacco composite use indices-as well as lifetime use of alcohol, cigarettes, and marijuana-and lifetime drunkenness, were examined. Significant intervention-control differences were observed, indicating favorable delays in initiation in the intervention groups.