To conduct a meta-analysis summarizing the effectiveness of school-based brief alcohol interventions (BAIs) among adolescents and to examine possible iatrogenic effects due to deviancy training in group-delivered interventions, a systematic search for eligible studies was undertaken, current through December 31, 2012. Studies were eligible for inclusion if they used an experimental/quasi-experimental design; focused on school-based BAIs; enrolled adolescent participants; and reported an alcohol-related outcome measure. Studies were coded for key variables, and outcome effect sizes were analyzed as standardized mean differences adjusted for small samples (Hedges' g). Analyses were conducted using inverse-variance weighted mixed-effects meta-regression models. Sensitivity analyses were also conducted. Across all 17 studies eligible for inclusion, school-based BAIs were associated with significant improvements among adolescents, whereby adolescents in the BAI groups reduced their alcohol consumption relative to the control groups (= 0.34, 95 % CI [0.11, 0.56]). Subgroup analyses indicated that whereas individually-delivered BAIs were effective (= 0.58, 95 % CI [0.23, 0.92]), there was no evidence that group-delivered BAIs were associated with reductions in alcohol use (= -0.02, 95 % CI [-0.17, 0.14]). Delivery format was confounded with program modality, however, such that motivational enhancement therapy was the most effective modality, but was rarely implemented in group-delivered interventions. Some school-based BAIs are effective in reducing adolescent alcohol consumption, but may be ineffective if delivered in group settings. Future research should explore whether group-delivered BAIs that use motivational enhancement therapy components may yield beneficial outcomes like those observed in individually-delivered programs.