Background  There is recent interest in using music making as an empirically supported intervention for various neurodevelopmental disorders due to music's engagement of perceptual–motor mapping processes. However, little is known about music learning in populations with developmental disabilities. Williams syndrome (WS) is a neurodevelopmental genetic disorder whose characteristic auditory strengths and visual–spatial weaknesses map onto the processes used to learn to play a musical instrument. Methods  We identified correlates of novel musical instrument learning in WS by teaching 46 children and adults (7–49 years) with WS to play the Appalachian dulcimer. Results  Obtained dulcimer skill was associated with prior musical abilities (r = 0.634, P < 0.001) and visual–motor integration abilities (r = 0.487, P = 0.001), but not age, gender, IQ, handedness, auditory sensitivities or musical interest/emotionality. Use of auditory learning strategies, but not visual or instructional strategies, predicted greater dulcimer skill beyond individual musical and visual–motor integration abilities (β = 0.285, sr2 = 0.06, P = 0.019). Conclusions  These findings map onto behavioural and emerging neural evidence for greater auditory–motor mapping processes in WS. Results suggest that explicit awareness of task‐specific learning approaches is important when learning a new skill. Implications for using music with populations with syndrome‐specific strengths and weakness will be discussed.