Background: The self-esteem and school experiences of mixed-race adolescents in the United Kingdom is overlooked in research, despite studies showing mixed-race adolescents may have poorer mental health outcomes than their monoracial peers (e.g. Wong et al., 2012). Aims: This study explored if and how the school experiences and self-esteem of mixed-race girls differed from monoracial peers, and potential mechanisms accounting for differences in self-esteem. Sample: Quantitative questionnaires (Phase 1) sampled 109 girls (M[subscript age]=13.9 years). Interviews (Phase 2) sampled 12 mixed-race girls (M[subscript age]=14.3 years). Methods: This study used a mixed-methods design. Phase 1 examined self-esteem scores, prevalence of peer-based discrimination, and related support factors (ethnic identity exploration and affirmation, peer support and friendship diversity). Phase 2 involved semi-structured interviews. Results: Mixed-race girls reported lower self-esteem than monoracial peers from Black and Minority Ethnic (BME) backgrounds. Friendship support predicted mixed-race girls' self-esteem. Interview data showed that microaggressions (i.e. everyday comments communicating hostile racial messages), family racial socialisation practices (i.e. how youth learn about their own ethnicity and navigating racism) and school diversity were important in understanding the self-esteem of mixed-race girls. Conclusions: This study provides insight into adolescent mixed-race girls' school experiences and self-esteem, with implications for practitioners and families. We discuss areas for further research.