This article examines a unique music curriculum and assessment environment through the fndings of a practical action research project carried out in secondary schools. I address two current international educational issues: the relationship between formal and informal learning in music, and how individuals' contributions in collaborative groups might be summatively assessed. Following this I present a model of group composing and explain how it was used as a pedagogical tool in secondary music classrooms. The purpose of this was to help students and their teacher to conceptualise collaborative composing, thereby leading to a clearer understanding and more valid assessment of the processes in which they were engaged.