This article represents a replication and extension of previous studies of the effects of Project ALERT, a school-based substance use prevention program, on the prodrug beliefs of adolescents. Specifically, the authors' research examined Project ALERT's effects on adolescents' intentions to use substances in the future, beliefs about substance use consequences, normative beliefs, and resistance self-efficacy. In all, 34 schools with Grades 6 to 8 completed this randomized controlled trial and 71 Project ALERT instructors taught 11 core lessons to 6th graders and 3 booster lessons to 7th graders (one grade level earlier than in previous studies). Students were assessed in 6th grade prior to the onset of the intervention, in 7th grade after the completion of the 2-year curriculum, and again 1 year later in 8th grade. The authors found no evidence to suggest that Project ALERT had a positive impact on any alcohol, cigarette, or marijuana prodrug beliefs. Implications for school-based substance use prevention are discussed.