<p>Social norms campaigns have been used as an intervention to address common concerns, such as bullying and sexual harassment, in high schools. While there is promise for their use, there have been mixed results in terms of creating change in students’ attitudes, and there is scant evidence about variables that may contribute to these outcomes. Based on a sample of 359 students (82% White, 53% Female) from a suburban high school in the Northeastern United Stated participating in the pilot of a social norms campaign to reduce bullying and sexual harassment, this study examined whether acceptability of, believability of, and exposure to campaign messages contributed to changes in individuals’ perceptions of their peers’ attitudes. Believability and acceptability of the campaign were significant predictors of change, with students who reported greater campaign believability and acceptability also reporting greater levels of change in their perceptions of their peers at post-test. White students and straight students showed greater change in their perceived peer norms compared with their non-White and sexual minority (SM) peers. This study highlights the importance of student input in the development of campaigns, particularly in taking measures to improve students’ perceptions of believability and acceptability of a social norms campaign. </p>