PROJECT SUMMARY/ABSTRACT Sexual violence has overwhelming costs and consequences that necessitate primary prevention solutions. More than 52 million women (43.6%) and 27 million men (24.8%) in the U.S. experience some form of sexual violence in their lifetime including rape, sexual coercion, and/or unwanted sexual contact. Adolescence is a critical time for first experiencing sexual violence, as 40% of women with a history of rape first experienced it before age 18. These experiences have lifelong negative health consequences. Most sexual violence prevention programs have been developed for mid- to late-adolescence or for college students, when sexual violence is most prevalent. Yet, effective interventions to prevent sexual violence among adolescents and before it occurs are rare, lack adequate evidence, are individual-focused, and are resource intensive. Washington State's new Youth-centered Environmental Shift (YES!) program, developed by the Washington Office of Superintendent of Public Instruction is based on the best available evidence for preventing sexual violence at the level of a whole school community. The overall goal of YES! is to create a culture within middle schools where students are emotionally and physically safe, supported, and free of abuse, specifically sexual violence. The program is focused on preventing sexual violence before it begins and providing a school-wide program that is effective and scalable to other schools. YES! will be piloted in Washington middle schools in 2020 through collaboration with one Educational Service District in Washington, serving 44 school districts. Through strong partnerships with state agencies and schools, the study we propose will have two main components. First (Component A), we will build system-level capacity to effectively examine the impact of YES! in the three pilot middle schools, establish collaborative systems for collecting sensitive data from students and staff, and assess the feasibility and acceptability of the YES! pilot. Second (Component B), we will expand our evaluation process to more schools to rigorously evaluate whether YES! reduces violence victimization and perpetration, has an impact on the risk and protective factors associated with sexual violence, and if it is feasible for YES! to be sustained and further scaled-up. We will use a practice-based approach that engages education partners and school personnel throughout our study, to improve the success of our approaches, interpretations, study applications, and translation to practice. In this second component we will use a group randomized design, randomly assigning middle schools to initiate the YES! program or proceed with their `usual practice' around sexual violence prevention. This design will be used to rigorously evaluate the impact of YES! on sexual violence outcomes. Data collected through surveys and focus groups of middle school students and staff at multiple points in times over the full five years of t...