Peer-mediated interventions (PMIs) offer substantial academic and social benefits to adolescents served under the special education categories of intellectual disability, autism, and multiple disabilities (i.e., intellectual and developmental disabilities [IDD]). However, limited attention has focused on the impact of PMI on participating peers without disabilities. This systematic review identified all experimental (e.g., single case, group experimental) and descriptive (e.g., qualitative, survey) studies addressing PMIs implemented at the secondary level with students with IDD. Among the 98 PMI studies that we identified in this review, 66 (67.3%) studies included some qualitative or quantitative measure of peer impact. Across these studies, the impact on peers was addressed in 10 different areas. This review provides new insights into the ways peer impact has been evaluated and how peers have been impacted by their PMI experience. Recommendations for research and practice aimed at addressing the benefits of involving peers without disabilities in these interventions are provided.