Objectives. Our purpose was to investigate the processes involved in, and outcomes of, implementing 3 new state-level, school-oriented childhood obesity policies enacted between 2004 and 2007. Methods. We followed policy implementation in 8 high schools in Mississippi and Tennessee. We collected data between 2006 and 2009 from interviews with policymakers, administrators, teachers, and students; observations of schoolbased activities; and documents. Results. Significant barriers to the effective implementation of obesity-related policies emerged. These most notably include a value system that prioritizes performances in standardized tests over physical education (PE) and a varsity sport system that negatively influences opportunities for PE. These and other factors, such as resource constraints and the overloading of school administrators with new policies, mitigate against the implementation of policies designed to promote improvements in student health through PE. Conclusions. Policies designed to address health and social problems in highschool settings face significant barriers to effective implementation. To have a broad impact, obesity-related policies must be tied to mainstream educational initiatives that both incentivize, and hold accountable, the school-level actors responsible for their implementation.