This study describes and analyses how coteaching affected undergraduate music education preservice teachers (PSTs). During an 8-week school placement, coteaching was used as a means of creating a reciprocal professional learning arrangement involving PSTs and primary school teachers. The theoretical framework draws on the Russian concept of "obuchenie," which is a dialectical process of mutual adaptation between student and teacher. Music education PST participated as subject expert/pedagogy novice, while generalist classroom teacher occupied the role of pedagogy expert/music novice. Findings relate to the acquisition of four aspects of teacher professional agency, "subject or content knowledge," "pedagogical knowledge," "curricular knowledge," and "pedagogical content knowledge." A thematic analysis was undertaken using data from interviews, PST reflective journals, observations, lesson plans, and researcher field-notes. In comparison with the traditional school placement, there was a radical improvement in the development of professional agency amongst the coteaching cohort.