Postsecondary education students with intellectual and multiple disabilities are often supported by same-aged peer mentors. A single-subject multiple baseline design was used to examine the relationship between training with and without performance feedback and a peer mentor's fidelity of implementing a student's function-based intervention plan across settings. Further, the relationship between peer mentor fidelity and a student's on-task behavior was explored. The peer mentor's fidelity immediately improved in all settings after being trained but required performance feedback to improve further. There was a functional relation between the peer mentor's fidelity and the student's behavior in two of the three settings.