760 children aged 8 to 12 composed 1,696 short melodies using a computer- based software application. As well as providing an appropriate composing environment, the software maintained a detail event-driven log of all user interactions. Session logs were used as the basis of a detailed behavioural analysis of children's composing processes, exploring the influence of three variables (age, task familiarity and formal instrumental music tuition) on composing processes. Results suggested that older children tended to engage in less exploratory composing behaviour in comparison to younger participants, such as listening to their emerging melodies or trying out different notes. Participants receiving formal instrumental music tuition were far less likely to use the exploratory functions of the software in comparison to their non-expert peers. Older children worked faster than younger children, and were more efficient in their use of the software functions. Increased familiarity with the software was accompanied by greater speed in interaction, regardless of instrumental expertise. Implications for music composition pedagogy and future research in musical creativity are discussed