Physical activity is important for children’s development; low physical activity can negatively impact physical and mental health. Previous research has found children are not meeting current physical activity levels with large inequalities between children, particularly between girls and boys and those from different socio-economic backgrounds. To date interventions have been unsuccessful in addressing these issues. My research aims to address this by using a mixed-method and interdisciplinary approach, before co-designing an intervention to increase primary school children’s physical activity levels.