Objective Depressive disorders in adolescents are a widespread problem with extensive psychosocial consequences. The authors designed a school-based program to prevent the increase in depressive symptoms. The authors expect the program to reduce dysfunctional automatic thoughts and improve social skills and thus prevent the increase in depressive symptoms. Method The design includes a training group and a nontreatment control group with pre- and post-measurement and 3- and 6-month follow-up. The authors followed up 324 eighth graders in both groups. School classes were randomly assigned to one of the two groups. The prevention program, LISA-T, is based on cognitive-behavioral therapy concepts and targets of cognitive and social aspects. It comprises 10 meetings of 1.5 hours in a regular school setting. Results Increases in depressive symptoms in nondepressed adolescents in the training group were prevented over a 6-month period. Furthermore, adolescents with subsyndromal depression in the training group reported fewer symptoms, whereas depressive symptoms within the control group did not change. However, the groups did not differ with regard to social skills, frequency of negative automatic thoughts, and depressive symptoms before the prevention program. Conclusions LISA-T is an effective school-based prevention program for eighth graders with minimal to mild depressive symptoms, but further research is needed.