Students with autism spectrum disorder (ASD) have marked deficits in social communication skills, which can challenge their ability to participate in academic and social activities. Music therapy is a popular intervention for children with ASD, and although research evidence supporting its effectiveness is growing, methodological flaws limit interpretation. The present study proposes a new measure, the DUACS, to assess outcomes associated with a group music therapy program, Voices Together. Participants were 64 elementary students from nine self-contained autism classrooms who attended 16 weekly intervention sessions. Teacher-reported behavior questionnaires and direct student behavioral measures were administered at baseline, during, and after treatment. Increases in communication and social skills suggested program effectiveness, particularly among students with higher baseline skills. Further investigation of this program approach will help to better understand its mechanisms and for whom it works best.