To date, most early intervention programs have been based on emotion regulation strategies that address dysfunctional cognitive appraisals, problem-solving sldlls, and rumination. Another emotion regulation strategy, 'acceptance' training, has largely been overlooked. To examine the efficacy of this strategy, a school-based mental health program combining positive psychology with acceptance and commitment therapy (Strong Minds) was evaluated in a randomized controlled trial with a sample of 267 Year 10 and 11 high-school students in Sydney, Australia. Mixed models for repeated measures examined whether the program led to reductions in symptoms amongst students who commenced the program with high depression, anxiety, and stress scores, and increased wellbeing scores amongst all students. Results demonstrated that compared to controls, participants in the Strong Minds condition with elevated symptom scores (n = 63) reported significant reductions in depression (p = .047), stress (p = .01), and composite depression/anxiety symptoms (p = .02) with medium to strong effect sizes (Cohen's d = 0.53, 0.74, and 0.57, respectively). Increased wellbeing (p = .03) in the total sample and decreased anxiety scores (p = .048) for students with elevated symptoms were significant for Year 10 students with medium effect sizes (Cohen's d = 0.43 and 0.54, respectively). This study tentatively suggests that including the emotion regulation strategy of acceptance in early intervention programs may be effective in reducing symptoms and improving wellbeing in high school students. Further research to investigate the generalizability of these findings is warranted. (C) 2016 Society for the Study of School Psychology. Published by Elsevier Ltd. All rights reserved.