Students qualifying for services under the Individuals with Disabilities Education Act may experience challenges meeting the socioemotional demands of the school environment, creating a need for targeted interventions that can be delivered within school settings. The current study used a mixed-methods approach to examine the efficacy of a 4-week school-based musical theater intervention delivered to 121 elementary students with intellectual and developmental disabilities. Quantitative analyses of teacher-reported changes in student engagement pre- and post-intervention were conducted to compare student gains made across two intervention curricula, followed by qualitative content analyses of teachers' responses to open-ended survey questions. Results indicated an overall benefit of the musical theater intervention, with increases found in composite scores on the teacher-report Student Engagement Survey measure after completion of both intervention curricula; however, gains in individual survey item scores differed by curricula. Additionally, qualitative analyses provided positive insight into several aspects of the intervention.