The overall aim of the present study was to further our understanding of how family characteristics and parental factors influence children's beliefs, motivation and participation in instrumental music. The study was a longitudinal survey design to allow data to be collected from both parents and children in Year 6 at primary school and Year 7 at secondary school, in order to monitor change in the belief, behaviour and participation constructs across the transition period. The longitudinal design also enabled testing of whether beliefs and behaviour constructs at primary school (Time 1) predicted children's motivation and participation at secondary school (Time 2). The study had 506 parent and child participants at Time 1 and 126 participants at Time 2. An expectancy-value model of parental influence on children's motivation and participation in instrumental music was developed for the study and tested for the first time with path analysis. The results have added to our understanding in several key areas. Family socioeconomic status, parent efficacy beliefs, and children's gender were found to have strong influence across the model to children's aspiration to play an instrument, but were mediated through children's own competence beliefs and perception of parent value and support for music, suggesting that there is a need to explore the wider context of both parent and child beliefs in this domain. The model was not found to predict children's participation, suggesting that children's perceptions and beliefs may have a stronger influence on their participation in music than some other domains where parental influence was found to be direct as well as mediated through children's beliefs. The findings also offer suggestions of factors which may insulate children from abandoning music after the transition to secondary school, along with directions for future research