Public policies impact the amount of physical activity (PA) that children receive at school. These policies are of interest because overweight and obesity among Canadian children have grown at significant rates, and increasing PA among children is one way to reverse this trend. This research investigates the public policy processes that have resulted in Alberta's education system adopting in-school daily physical activity (DPA) and not supporting walk-to-school (WTS) initiatives. Using the policy process described by Kingdon and others as a conceptual framework, this research reviews literature and documents on public policy relating to PA in schools and interviews key individuals (N = 20) to identify the policy-related facilitators and barriers in Alberta, Canada to increasing PA in school-aged children. DPA was mandated because Kingdon's three policy streams (problem, solution and politics) became joined or linked. DPA was the most viable solution because literature supports and teachers believe in the educational benefits of PA. As well, a physician with personal beliefs about the benefits of PA became the minister of education and coupled the solution with the political stream through his ministerial power. Reasons that WTS programs have not become school or health policy include advocacy led by politically weak organizations, lack of a supportive policy entrepreneur and poor saliency among educators. This research illuminates the inner workings of the policy process shaping PA in schools, identifying the unseen forces of the policy process that move issues forward. The findings provide valuable insight for building other healthy public policies.