This study examined 44 students' engagement in the composition of popular and classical music in a computer-mediated environment. The study took place over the course of one school year at a government-funded secondary school in Hong Kong that had 30 iMac music workstations. Participants were 22 Form 3 students (aged 14-15) and 22 Form 4 students (aged 15-16) who composed in different genres consisting of popular music styles and classical music styles (i.e. baroque, classical and romantic period music), respectively, on the computer as part of the school's music curriculum. At the end of the study, participants completed a retrospective assessment to examine the correlation between engagement in music learning and computer-mediated composition. The results indicated three areas that should be considered in music curriculum development: 1) sustainable engagement in learning both classical and popular music; and 2) the idea of 'de-composing' and 're-composing' pedagogy in both classical and popular music styles. The findings suggest that 'de-composing' and 're-composing' pedagogy in computer-mediated composition may engage students in ways that promote deeper learning by combining 'old' and 'new' musical styles through an engagement cycle that enhances an understanding of both classical and popular music.