This randomized controlled trial examined the efficacy of peer network interventions to improve the social connections of 47 high school students with severe disabilities. School staff invited, trained, and supported 192 peers without disabilities to participate in individualized social groups that met throughout one semester. Compared to adolescents in the “business-as-usual” control group (n = 48), students receiving peer networks gained significantly more new social contacts and friendships. Although many peer relationships maintained one and two semesters later, their spill over beyond the school day was limited. Students and staff affirmed the social validity of the interventions. We offer recommendations for research and practice aimed at improving the implementation and impact of peer network interventions in secondary schools.