This article reports a qualitative study of co-creation in high school music education conducted in a public Polish high school. The analysis focuses on three co-created projects: a narrative concert that helped form a choir, a student-initiated ballet combining live and recorded music, and a film-music festival led by students. The objectives were to examine how participation in collaborative projects develops student agency and responsibility; to identify school conditions that support a culture of co-creation; and to describe how the teacher’s role changes from leader to mentor and partner.The study used a qualitative action-research approach with approximately students aged 16-18. Data sources included participant observation of rehearsals, meetings, and performances; short group and individual interviews after each project; and document analysis (project plans, programmes, posters, rehearsal notes, and internal online communication). The material was examined using thematic analysis. Ethical procedures covered informed consent, voluntary participation, and confidentiality.Results indicate a clear progression in student agency. In the first project, students contributed creative ideas while the teacher organised and guided work. In the second, students took on artistic and organisational tasks such as arranging, simple choreography, promotion, and stage preparation, inviting the teacher to conduct the performance. In the third, students led most activities, including drafting regulations, scheduling, managing sound and lighting, and hosting the event. Supportive conditions included trustful teacher-student relations, respectful dialogue, peer learning in mixed-experience groups, transparent division of tasks, brief regular reflections, and light use of digital tools for coordination. The teacher’s role evolved from organiser to mentor and advisor, stepping in only when needed. Emotions—joy, pride, and pre-performance stress—formed part of learning and helped build a strong sense of community.The study concludes that co-creation is a practical approach that balances structure with freedom. When students receive meaningful choices and responsibilities within a supportive school culture, music education becomes a shared space of discovery that advances musical achievement together with collaboration, reflection, and social engagement.