With colleagues in Japan, the author, a composer and improvising musician, developed novel techniques of collaborative composition. Subsequently – in Japan and in Britain – he explored ways of developing those techniques with school pupils. In this article he writes about the background to that experiment, the professionalism of composers and performing musicians, and the relative importance of boundaries of all kinds (e.g. different frames for the reception of music). In particular, he reflects upon compositional ideas and processes generated by his work with children.