Identity forms for the first time in adolescence (McLean & Syed, 2015) and is a foundational component of the capacity to live a healthy life (Erikson, 1968; Marcia, 1980). Forming a stable identity is the central task of adolescence, the developmentally critical period between childhood and adulthood (e.g., Erikson, 1968; Luyckx et al, 2005). Scholars have investigated musical identity as a framework for understanding how individuals personally experience music as a function of their identities (Hargreaves et al, 2002; 2016). While some have examined music and adolescence (Parker, 2020), the relationship between identity development (ID) and musical identity (MI) remains underexplored. No research to date has addressed how adolescent musical identity might specifically influence identity development. Accordingly, this study investigates these dynamics through the lens of Erikson's theories of identity development and Marcia's identity status theory. The purpose of this intrinsic case study (Stake, 1995) was to understand how adolescent middle school musicians constructed their musical identities at a developmentally-oriented school. Data collection took place from January - July 2024 at the Orchard Hills School, a progressive, urban K-8 school with mandatory orchestra participation. Participants included adolescent students (n=16) as well as parents (n=9), music teachers (n=2), and administrators (n=4). The data set featured 26 hours of interviews, 30 hours of classroom observations, material culture, and handwritten student reflections. Analysis deployed in vivo coding to prioritize participants’ original phrasing and seven validation strategies to ensure thorough representation and analysis. Findings revealed musical agency as the prerequisite for musical identity development. Students with more musical agency were significantly more likely to view themselves as musical, engage with music across multiple contexts, and express interest in future participation. Students with affective definitions of musicality (based on feeling and connection) were more musically engaged and held more integrated musical identities than students with behavioral definitions (based on technical skill).These conclusions challenge definitions of musicality that reify technical achievement over personal growth, thus offering music educators a chance to better support adolescents in their most developmentally important and emotionally vulnerable moments (Sahi et al, 2023). True inclusivity in music education may require reconceptualizing ensembles to center students’ agency. Schools that help adolescents to not only be “good” at music but to love music, and love the process of “finding their peace” with it (Parker, 2020, p. 235) are worthy of serious scholarly investigation, particularly in these challenging times. When adolescents experience music-making as a space for exploration, social connection, and authentic self-expression, they are more likely to develop sustainable, integrated musical identities that extend beyond the classroom into their greater lives.