Research on student willingness to report peer weapon carrying points to the importance of school climate and contributions favorable to reporting. This study fills a gap by examining the etiology of willingness to report weapons on campus using predictors at the individual- and school levels. We utilize data from high school student self-reporting; results suggest that 34% of students reported having seen or having personal knowledge of a weapon in school in the prior 3 months. Students who report higher levels of school attachment, seeing or knowing of a weapon, have higher grades, and know about security measures were significantly more likely to report seeing weapons. Implications are discussed.