Co-curricular activities have been shown to impact many measures of academic success, such as academic self-confidence, leadership abilities, identity development, personal development, and student thriving. Borrowing from established research paradigms on pluralistic ignorance, the current study sought to explore whether first-year and senior students' perceptions of themselves and others vary when it comes to attending and participating in campus activities and whether sex has an impact on those perceptions. Using data from the 2018 National Survey of Student Engagement, the study included 10,512 students attending 33 institutions. The results suggest significant differences across the sexes and within reference group (self vs. other) for attending campus activities and participating in co-curricular activities. These findings can help guide faculty, advisors, and administrators to better understand how students' perceptions of peer co-curricular activities might relate to their own, and how those perceptions might affect their behavior positively and negatively.