Only 12% of UK 14-year-old girls meet physical activity guidelines. In our survey study with >2,000 girls, 46% of girls reported that their breasts affected their sports participation and73% reported ≥ one breast-specific concern in sports, with breast bounce being most prevalent. Furthermore, 26% of girls reported negative feelings about their breasts and 87% want to learn more about their breasts. This study aims to evaluate the short- and long-term impact of a 50-minute comprehensive breast education intervention on girls’ breast knowledge and attitudes towards breasts and breast issues. A mixed method, controlled, longitudinal-cohort-design was employed: two control schools (receiving no intervention) and two intervention schools (receiving the intervention) participated in the study. All four schools completed a validated breast survey pre- and post-intervention, as well as three and six months after the intervention. Additionally, in one intervention school, six focus groups were conducted post-intervention and ~four months after the intervention. Analysis of survey data established the short- and longterm positive impact of the intervention; participants in the intervention schools (n = 375) significantly improved their breast knowledge, and their attitudes towards breasts over a sixmonth period, compared to participants in the control schools (n = 412). The focus group findings supported the survey results. Participants described the session as informative and it made them feel less embarrassed about their breasts; they also reported wanting to do more exercise. These findings demonstrate the positive impact of the intervention which may have the potential to impact policy change and inform education guidelines.