This article examines the relationship between the professional learning of music teachers and their capacity and opportunity to act and engage agentically with the structures and discourses of music education. The authors begin by drawing on a range of education and music education scholarship to examine the concepts of teacher autonomy, teacher agency and professional development. They propose a socio-cultural understanding of teacher agency which draws on Gidden's theory of structuration and Priestley, Biesta and Robinson's ecological approach. Here, the relationship between structure and agency is not determinant but dynamic, with teacher agency dependent on the extent to which music teachers are able to engage in the discourses of music education. They explore the way professional development structures and policy in England and China affect teacher agency and especially how policy developments, the changing structures of music education, and the fetishization of advocacy narratives have constrained and marginalized the voice of the classroom music teacher. The authors conclude with a call for music teacher professional development to support music teachers to act agentically through reengaging with the epistemological and ontological dimensions of music and the policy discourses of music education.