The purpose of this mixed-methods study was to explore the phenomenon of participation in a high school rock orchestra from the perspective of alumni. Specific research questions addressed the musicians' reflections on experiences in the rock orchestra and the perceived possible impact on their current musical and professional lives. Survey and interview results provided a retrospective portrait of membership in the ensemble and what young adult members indicate was valuable, helpful, transformative, and transferable about participation in the rock orchestra. Textural elements of experiential learning, social-emotional processes, and skills for life were supported by structural elements of informal learning practices and a dialogue between Western classical and rock music traditions. This led to the essence of involvement identified as multi-dimensional growth through experience in a rich musical environment. We discuss whether informal learning practices may spur students to continue making music after they have left the structured environment of a school music program, the impact of student agency in their own musical space, and ways in which the rock ensemble might provide an example for integrating informal learning practices into existing school music ensemble programs.