This study evaluated the Penn Resiliency Program's effectiveness in preventing depression when delivered by therapists in a primary care setting. Two-hundred and seventy-one 11- and 12-year-olds, with elevated depressive symptoms, were randomized to PRP or usual care. Over the 2-year follow-up, PRP improved explanatory style for positive events. PRP's effects on depressive symptoms and explanatory style for negative events were moderated by sex, with girls benefiting more than boys. Stronger effects were seen in high-fidelity groups than low-fidelity groups. PRP did not significantly prevent depressive disorders but significantly prevented depression, anxiety, and adjustment disorders (when combined) among high-symptom participants. Findings are discussed in relation to previous PRP studies and research on the dissemination of psychological interventions.