BACKGROUND: Childhood physical inactivity and obesity are serious public health threats. Socioecological approaches to addressing these threats have been proposed. The school is a critical environment for promoting children's health and provides the opportunity to explore the impact of a socioecological approach. CONTEXT: Thirty percent of children in British Columbia, Canada, are overweight or obese, and 50% of youths are not physically active enough to yield health benefits. METHODS: Action Schools! BC, a socioecological model, was developed to create 1) an elementary school environment where students are provided with more opportunities to make healthy choices and 2) a supportive community and provincial environment to facilitate change at the school and individual levels. CONSEQUENCES: The environment in British Columbia for school- and provincial-level action on health behaviors improved. Focus group and project tracking results indicated that the Action Schools! BC model enhanced the conceptual use of knowledge and was an influencing factor. Political will and public interest were also cited as influential factors. INTERPRETATION: The Action Schools! BC model required substantial and demanding changes in the approach of the researchers, policy makers, and support team toward health promotion. Despite challenges, Action Schools! BC provides a good example of how to enhance knowledge exchange and multilevel intersectoral action in chronic disease prevention