Teaching and learning are complex processes and evaluating the work of music teachers is neither obvious nor simple. The outcomes of educational transactions may not be completely or immediately apparent. Furthermore, the contexts in which musical skills and understanding are acquired are multiple, going well beyond the formal categories of "general" class music teacher or the "private" instrumental and vocal teacher. In many of these alternative settings, standardised student assessment or teacher evaluation processes may be inappropriate. In this paper, an approach to evaluating teaching and learning draws on Swanwick's three principles for music educators. To these three principles is added the need to understand the educational and social context in which a teacher works. These criteria help to identify the "good-enough" teacher's contribution to students' musical development. The concept of the "good-enough" teacher is exemplified, not in the context of conventional formal teaching settings but in a third, much less defined role, that of music leader. The extent to which music leaders contribute to their musical environment is evaluated in a study of their continuing professional development. This evaluation was initiated by Youth Music, a UK organisation working alongside the formal and community-based sectors to support music-making and training.