Recently, models have been developed that recognise the complexity of motivation. These set out the interactions that occur between environmental (cultural, institutional, familial, educational) and internal factors (cognition and affect) enhancing or reducing motivation. Despite this we know very little about gender differences in motivation in relation to playing an instrument. The current study aimed to address this issue, exploring gender differences in motivation and whether these changed as expertise developed. A total of 3325 children ranging in level of expertise from beginner through to Grade 8 level in independent instrumental music examinations completed a questionnaire that included a seven-point Likert scale with statements exploring different aspects of motivation. A principal components analysis was undertaken and six factors emerged: support and social affirmation; social life and enjoyment of musical activities; enjoyment of performing; self-beliefs; enjoyment of lessons, playing and practise; and disliking practise. The only statistically significant gender difference was in relation to self-beliefs with the boys consistently scoring higher. Further research is needed to establish why this is the case. The findings have major implications for education.