Abstract: Sexual violence (SV) occurs along a continuum of severity ranging from sexual bullying, harassment, unwanted sexual touching, to completed physical rape.1 Risk for SV victimization begins very early in life:1-3 by 12th grade, 12% of girls and 4% of boys have been physically raped.2 Rates are higher among sexual/gender minority youth (SGMY) with 23% of SGMY girls and 10% of SGMY boys reporting rape victimization. Notably, the majority of adolescent SV victims' perpetrators are their peers4-5 with nearly half of all victimization occurring on school campuses.5-6 Growing evidence suggests that social norms that condone bullying and sexual harassment may give rise to the perpetration of more severe forms of SV.75 The “Step Up, Step In” (SUSI) program, is a social marketing campaign to prevent SV among adolescents. Guided by social norms theory, the SUSI campaign aims to promote social norms that protect against sexual bullying, harassment, and SV. SUSI implementation is funded by the Georgia Department of Public Health under CDC's Rape Prevention and Education (RPE) initiative (RFA-CE19-1902). It has been implemented in 42 schools across 19 counties in Georgia since 2014. However, there have been no evaluations of social marketing campaigns as SV prevention strategies for adolescents, including the SUSI program. This gap in the field is critical given the accelerating rate of onset for SV victimization that occurs during and within high schools.4-6 Given SUSI's current sustained phase of implementation, it is an ideal candidate to evaluate for SV prevention. We will implement a sequential tri-phased evaluation plan that progresses from formative to rigorous summative evaluation. Stage 1 (years 1 & 2), we will conduct interviews with students and staff to assess the clarity, saturation, acceptability, feasibility, buy-in, salience, and reaction to campaign content. Findings from this phase will inform any revision to SUSI campaign deemed necessary to increase buy-in and impact on SV for both cis-gender heterosexual and SGMY. We will also conduct quantitative surveys with a random subsample of students from both SUSI and non-SUSI schools to assess the rates of SGMY, rates of SV, and rates of dating and sexual behavior. This survey will also assess the current social norms pertaining to sexual bullying and violence, social norms about SGMY, gender equity, and school climate. Stage 2 (year 3), we will implement a small pilot evaluation of the SUSI program to obtain estimates of 1) recruitment response rates, 2) attrition rates, 3) effect sizes, 4) rate of sample shrinkage from propensity score matching. Stage 3 (years 4 and 5), we will implement a full-scale rigorous evaluation of the SUSI program with a cohort of freshman from 2 intervention and 2 comparison schools. Youth will be surveyed 4 times over 2 years. Because the SUSI program is in the sustainability phase of implementation, we cannot randomize the intervention. We will therefore use...