Lack of relevancy, administrative support, collegial support, and time are just a few of the many barriers that prevent practicing music teachers from accessing relevant professional development (PD) and taking steps to improve their practice. Quality music education PD should help teachers transform practice to improve student learning. Some characteristics of impactful PD include long-term engagement, teacher-to-teacher collaboration, and context-specific classroom implementation and documentation. In this intrinsic case study, we examined the role of a collaborative PD group designed to guide music teachers in using the reflection-on-action cycle to make improvements in their middle-level general music practice. Results from this project suggest that the reflection-on-action cycle is useful for PD projects that focus on improving classroom practice and empowering teachers with autonomy and choice. Teacher-to-teacher collaboration may also support teacher resilience during project difficulties.