There are many mandated school-based programs to prevent adolescent alcohol and drug (AOD) use, but few are voluntary and take place outside of class time. This cluster randomized controlled trial evaluates CHOICE, a voluntary after-school program for younger adolescents, which reduced both individual- and school-level alcohol use in a previous pilot study. We evaluated CHOICE with 9,528 students from 16 middle schools. The sample was 51% female; 54% Hispanic, 17% Asian, 15% white, 9% multiethnic and 3% African American. Fifteen percent of students attended CHOICE. All students completed surveys on alcohol beliefs and use at baseline and 6-7 months later. We conducted intention-to-treat (ITT) school-level analyses and propensity-matched attender analyses. Lifetime alcohol use in the ITT analysis (i.e., school level) achieved statistical significance, with an odds ratio (OR) of 0.70 and a NNT of 14.8. The NNT suggests that in a school where CHOICE was offered, 1 adolescent out of 15 was prevented from initiating alcohol use during this time period. Although not statistically significant (p = .20), results indicate that past month alcohol use was also lower in CHOICE schools (OR = 0.81; NNT = 45). Comparisons of attenders versus matched controls yielded results for lifetime use similar to school-wide effects (OR = 0.74 and NNT = 17.6). Initial results are promising and suggest that a voluntary after-school program that focuses specifically on AOD may be effective in deterring alcohol use among early adolescents; however, further research is needed as program effects were modest.