The World Health Organization advises that adolescents engage in at least 60 minutes of moderate to vigorous physical activity daily. However, a significant proportion of adolescents do not meet this recommendation, with a notable gender gap. Specifically, 92% of girls fall short of this target, compared to 82% of boys. Physical education programs often exacerbate these inequalities. This study aims to investigate, within the ecological framework, the conditions that exacerbate or mitigate gender differences in physical activity engagement during physical education classes. The study is based on a mixed methodology, combining quantitative measures (accelerometers, questionnaires) and qualitative measures (focus groups). Results showed that the odds of girls engaging in high levels of MVPA were substantially lower than those of boys (OR ≈ 0.65), particularly during performance-oriented and opposition activities. Gender disparities were also more pronounced in advantaged and urban schools, whereas rural and lower-SPI contexts showed smaller gaps. Qualitative data revealed that girls often experience social discomfort and judgement, particularly from boys, which undermines their participation. These findings emphasise the importance of rethinking PE practices through an ecological lens by considering the interplay between activity type, school context and social dynamics, to foster more inclusive engagement for all students