Sociological research investigating boys' masculinity performances has commonly recognised the importance of peer group cultures in identity construction. Whilst such work has undoubtedly offered important and useful frameworks for interpreting and understanding boys' behaviour in schools, the article argues that social psychological theories of intergroup relations also proffer important insights. Drawing upon interview and survey data, the article focuses on the existence of intergroup bias between peer groups in two secondary schools and demonstrates how a social identity framework can assist in providing a fuller and more complex understanding of boys' masculinities than sociological insights alone. Furthermore, it is suggested that gender work strategies designed to address and ultimately help some boys restructure their constructions of masculinity, which recognise the range of complex sociological "and" social psychological processes at work, are likely to more effective than those that offer partial insights. As such, strategies that draw upon work on masculinities and upon social psychological theories of intergroup relations may be particularly effective. (Contains 2 tables and 6 notes.)