Background: High prevalence rates of mental disorders and its impairment in affected children and adolescents indicate the necessity of prevention programs. Methods: The primary goal was to develop, implement, and evaluate a modularized prevention program with a focus on emotional competence that can be conducted by students (service learning concept). The sample consisted of 1,195 children (M = 11.5 years, SD = 2.42) with 53% boys, 38 teachers (M = 45.76 years, SD = 9.49), and 188 group leaders (M = 23.38 years, SD = 2.61). Acceptance rates, self-efficacy, stress management, emotion regulation, and the increase of knowledge in a pre-post design were assessed using self-report questionnaires. Results: Teachers, children, and students reported high acceptance rates. In all three groups, recommendation rates ranged from 82 to 93%. A t test for dependent samples showed a small effect for an increase of constructive-palliative emotion regulation (t(97) = 2.62, p = 0.025, d = 0.29). There were no significant effects in the other outcome measures. Conclusion: Results indicate a successful implementation of a modularized prevention program. The strength of the modularized conception of a prevention program is the naturalistic study design and good transferability into practice, at the cost of internal validity.