While creativity is a key element of contemporary curriculum frameworks around the world, it is still insufficiently fostered in formal education settings. This study analyzes a project for collaborative musical creativity, entitled The Sonorous Paella. Participants (N = 12) were eight Year 4 secondary students, two professional musicians, an artist-in-residence, and a music teacher. Drawing on a graphic musical score, the participants worked together for 1.5 months to produce a group composition and performance. They were provided with various sound producers (instruments, everyday objects, technological devices) and were encouraged to flexibly utilize the physical space to maximize collaborative participation. Field notes and pictures taken during working sessions and rehearsals, audio recordings from the final concert, and individual interviews with all participants were qualitatively analyzed. In response to the three study objectives, we conclude that: (1) the design of this collaborative project was consistent with current research-based creativity discourses; (2) drawing on the quality and originality of the final concert, the project fostered the musical creativity of the group; and (3) participants’ perceptions of and opinions about their creativity learning processes were unanimously positive. Our final aim is to inspire music teachers in designing curriculum units that foster collaborative musical creativity.