The purpose of this research was to investigate the experiences of instrumental music teachers in Designing Arts Instruction, a 4-day professional development course in a large urban school district. Specifically, I was interested in which activities participants (a) found most relevant and applicable to their current teaching situation, (b) believed would most benefit student learning, and (c) believed would contribute most to their overall music teacher development. Multiple forms of data were collected including participants' reflections, researcher-facilitator journal and field notes, and structured individual interviews. Curriculum development and rubric writing were relevant to participants' teaching situations and also engaged teachers' personal musicianship. Participants recognized creative activities as motivating for students. Collaboration emerged as the course feature that contributed most to participants' overall development. Those who plan and facilitate professional development might consider including aspects that invite collaboration, deep thinking, engagement, and reflection, particularly within the context of teachers' musicianship.