 Regular physical activity is important for children's physical and mental well-being and academic performance. Unfortunately, too many children are not moving enough. Globally, 50% of children don't meet the internationally recognized target of 60 minutes of daily moderate to vigorous physical activity. This rises to 4 out of 5 children in westernized high-income countries. While school systems and teachers can play a central role in providing high-quality physical activity and transform this statistic, at present, little guidance exists on what a true whole-school physical activity approach should look like. Now, researchers, policymakers, and practitioners from the UK have laid the groundwork for getting there. This is the Creating Active Schools Framework. Using experience-based co-design, 50 school experts recently gathered to co-create a comprehensive whole-school physical activity framework. These experts included teachers, headteachers, active school coordinators, public health specialists, active partnerships, national organizations, Sport England local delivery pilots, and UK and international researchers. Experts worked in same-and-then mixed-stakeholder groups as they undertook a six-phase design sprint using the UK Design Council's double-diamond approach. Drawing on their strong understanding of the research and practice-based evidence on what works and what doesn't within schools, groups began by identifying the components of a school system that would improve physical activity among pupils. Then, each group drew a framework. After feedback and revision of each new framework, participants voted on the final framework, the Creating Active Schools Framework, or CAS. For the first time, CAS integrates the key working parts of a whole-school physical activity system, emphasizing the value of establishing whole-school practice and ethos. Practice and ethos drive the work of five key stakeholders who operate within the school's physical and social environments. Combined, these influence the delivery of physical activity programs across seven opportunities within the school day. Some of these opportunities, such as classroom lessons and recess, are easier to influence than others, such as time spent with school clubs and family. Beyond individual schools, CAS identifies the importance of aligning national organizations and policies to deliver clear messages on the importance of physical activity, driving change by enhancing the capability, opportunity, and motivation of the system and stakeholders within. The CAS framework has already empowering schools in the UK and other countries to embed a whole-school approach to physical activity. To create whole-system change, CAS should be adopted within national policies to consolidate and align the work of organizations to deliver one clear message for whole-school physical activity implementation. Finally, if we achieve these aims, CAS can drive systems change for physical activity and improve the lives of children and young people.