PROJECT SUMMARY Adolescents urgently need efficacious skin cancer preventive interventions due to their poor use of sun protection and likelihood to tan intentionally. Schools offer the ideal setting for delivering skin cancer preventive interventions to large numbers of adolescents. Existing efficacious school skin cancer preventive interventions target young children (elementary school students), use a one-size-fits-all approach, and focus on either sun protection or tanning but not both. We designed a novel and personalized skin cancer preventive intervention for adolescents that is delivered in the school setting and includes complementary content delivered to parents and teachers. This multi-modal intervention builds on adolescents’ interest in novelty and need for highly personalized interventions. In our preliminary study of the intervention components with 1,573 students in 11 schools, we observed medium to large effects for sun protection behaviors and small to medium effects for tanning and sunburn, with increased adolescent sun protection and better control in intentional tanning and sunburn pre- to post-intervention. We propose a two-arm, cluster randomized trial to test the efficacy of the intervention we developed against standard education among 30 schools (10,250 students total). The in-class intervention sessions will be delivered through health education classes. The co-primary outcomes of the trial will be adolescent sun protection use and intentional tanning assessed via self-report questionnaire pre- intervention and at three follow-up timepoints through one year post-intervention. Secondary outcomes include objectively assessed ultraviolet radiation exposure and sunburn occurrence. Assessment timepoints will be seasonally timed and ambient UVR will be included as a covariate. We will also identify the mechanisms by which the intervention impacts adolescent sun protection use and intentional tanning. Through this project, we will also examine moderators of the intervention effects on sun protection and tanning outcomes in order to guide future tailoring of the intervention to maximize efficacy for potentially underserved groups. This project addresses the critical need for school-based skin cancer preventive interventions that both increase adolescent use of sun protection and decrease intentional tanning. The project will also lead to new scientific understanding of the theoretical mechanisms underlying intervention outcomes and moderators of the intervention effects, which will inform future tailoring of the intervention to better meet the needs of particular subgroups.