This paper brings together extensive data from 257 children to explore the relative importance of social-environmental factors during critical periods of children's musical development. The paper also presents preliminary findings from a follow-up of 20 of the most musically successful children 8 years later to determine which childhood factors predict differences in success as adult performers. Those children who continued to play an instrument started at an early age, had higher parental support in lessons, and had first teachers who were friendly but not too technically able. However, these factors alone were not sufficient to predict relative success in childhood. Successful childhood musicians also appear to need teachers who are 'not too relaxed' and also 'not too pushy' and they also need to do substantial amounts of practice. The follow-up study suggested, though, that successful adult performers were not those who did the most practice; rather, the successful adults were those who took part in more concert activities in childhood, did more improvisation, and who had mothers at home in their early years. The results are discussed in relation to theories of musical development and the changing influences of parents, teachers and peers.