Enhancing the social and learning experiences of students with severe disabilities in inclusive classrooms has been a long-standing focus of research, legislative, and advocacy efforts. The authors used a randomized controlled experimental design to examine the efficacy of peer support arrangements to improve academic and social outcomes for 51 students with severe disabilities in high school general education classrooms. Paraprofessionals or special educators recruited, trained, and supported 106 peers to provide individualized academic and social assistance to students with severe disabilities throughout one semester. Compared to students exclusively receiving adult-delivered support (n = 48), students participating in peer support arrangements experienced increased interactions with peers, increased academic engagement, more progress on individualized social goals, increased social participation, and a greater number of new friendships. Moreover, an appreciable proportion of relationships lasted one and two semesters later after the intervention had concluded. These findings challenge prevailing practices for supporting inclusive education and establish the efficacy and social validity of peer support arrangements as a promising alternative to individually assigned paraprofessional support.