Although it is often suggested that there are important connections between composing, performing and audience-listening, there is little evidence as to the nature of this relationship. In this paper we report research into the extent that musical understanding is symmetrically revealed and developed across the three activities. Our theory of musical understanding is based on the work of Swanwick, and assessment criteria derived from the work of Swanwick and Tillman (1986) made it possible to compare levels of musical cognition whatever the specific activity. A study of the musical work of twenty children in a music school in Belo Horizonte, Brazil, suggests that performance usually elicits lower levels of musical understanding, significantly different from either composing or audience-listening. It seems that performance can be problematic within the music curriculum unless students are able to work at a technical level where they are able to exercise interpretative judgement and make musical decisions. The findings support the claims for an integrated music curriculum comprising all three activities.