School-based drug prevention curricula constitute the nation's most prevalent strategy to prevent adolescent drug use. We evaluated the effects of one such curriculum, Project ALERT, on adolescent substance use. In particular, we sought to determine if a single effect on 30-day alcohol use, noted shortly following the completion of the 2-year program, could be detected 1 year later. We also looked for delayed effects on other outcomes of interest, namely lifetime alcohol use, and 30-day and lifetime use of cigarettes, marijuana, and inhalants. We employed a randomized controlled trial that used school as the unit of assignment. Thirty-four schools with grades 6-8 from 11 states completed the study. Seventy-one Project ALERT instructors taught 11 core lessons to sixth graders and 3 booster lessons to seventh graders. Students were assessed prior to the onset of the intervention, as sixth graders, after the completion of the 2-year curriculum, as seventh graders, and again 1 year later as eighth graders. This paper examines data from the pretest and final posttest. Using hierarchical nonlinear modeling, we found that our earlier effect on 30-day alcohol use did not persist. Further, we continued to find no effects for lifetime alcohol use and both the lifetime and 30-day use of cigarettes, marijuana, and inhalants. Our findings do not support the long-term effectiveness of Project ALERT, when delivered to sixth graders.