The Self-Efficacy for Musical Learning questionnaire was adapted and tested with 404 primary school children, producing a robust Cronbach alpha (0.87) and confirming a single underlying factor through exploratory factor analysis. Test-retest scores showed the measure's stability over a 9-month period. Data were collected on children's prior music experience, extracurricular activities, and typical daily activities. Children also completed the Short Warwick-Edinburgh Mental Well-Being Scale and the Strengths and Difficulties Questionnaire. Those currently engaged in music tuition (learning an instrument or singing) had significantly higher self-efficacy scores than children who were not, and overall, girls' scores were significantly higher than boys'. Correlations with various additional measures, including wellbeing and reading for pleasure, highlighted multifaceted relationships of self-efficacy to children's lives. Regression analyses revealed that prior experience with instrumental tuition was the strongest predictor of music self-efficacy for learning; prosocial behaviors predicted boys' scores, and well-being predicted girls' scores. (Contains 3 tables.)