Conservatoires train musicians to high levels of proficiency in performance and other 'principal study' disciplines, but often, teaching is perceived as a second-class profession, and little is known about how music students learn to facilitate music making in others. Yet, conservatoires have a responsibility to contribute to the development of the music education workforce. Building on Shulman's Pedagogical Content Knowledge model (PCK), two new constructs are created from data gathered through textual narratives and semi-structured interviews from over 100 music undergraduates who reflect on their instrumental teacher education in a UK conservatoire. Transferable Content Knowledge (TCK) encapsulates the transferable skills that students develop in a conservatoire setting, enabling them to become confident communicators and collaborators. Values-Based Knowledge (VBK) nurtures a sense of social responsibility, raising students' awareness of the professional qualities and behaviours necessary to forge positive relationships and create stimulating learning environments. The emergent 'Developing Pedagogical Knowledge' (DPK) framework offers scope to explore the transition from student to teacher across other phases of education and in other disciplines.