BACKGROUND: The positive relationship between parent-child interactions and optimal child development is well established. Families of children with disabilities may face unique challenges in establishing positive parent-child relationships; yet, there are few studies examining the effectiveness of music therapy interventions to address these issues. In particular, these studies have been limited by small sample size and the use of measures of limited reliability and validity. OBJECTIVE: This study examined the effectiveness of a short-term group music therapy intervention for parents of children with disabilities and explored factors associated with better outcomes for participating families. METHODS: Participants were 201 mother-child dyads, where the child had a disability. Pre- and post-intervention parental questionnaires and clinician observation measures were completed to examine outcomes of parental wellbeing, parenting behaviors, and child development. Descriptive data, t-tests for repeated measures and a predictive model tested via logistic regression are presented. RESULTS: Significant improvements pre to post intervention were found for parent mental health, child communication and social skills, parenting sensitivity, parental engagement with child and acceptance of child, child responsiveness to parent, and child interest and participation in program activities. There was also evidence for high parental satisfaction and that the program brought social benefits to families. Reliable change on six or more indicators of parent or child functioning was predicted by attendance and parent education. CONCLUSIONS: This study provides positive evidence for the effectiveness of group music therapy in promoting improved parental mental health, positive parenting and key child developmental areas.