Identifying ways to increase and sustain active living among young people represents a priority for health promotion interventions. This qualitative study explored the experiences of adolescent boys and girls in the United Kingdom (aged 14-15 years) who had made the transition from inactivity to active participation in physical education (PE). The setting was a secondary school that had modified the PE programme, with the aim of increasing participation rates. Thirty-one, self-identified, formerly "PE adverse" students were interviewed in focus groups in the school setting. Previously, respondents felt that they had been constructed as physically marginal individuals. Having a physically "marginal body" was perceived as being detrimental to emotional health. The new PE resulted in respondents possessing a performing and achieving physical identity. Boys gained a sense of security in their physical identity and cultural change had removed the aggression from interacting with other physically active peers. Girls spoke of increased self-confidence, including acquiring the psychological resources to participate in community-based activities. Effective health promotion interventions for inactive adolescents are likely to move beyond solely endorsing the benefits of physical activity or increasing choice and instead address the potential emotional risks and value of participation from the adolescents' perspective.