Background: In 2006, all local education agencies in the United States participating in federal school meal programs were required to establish school wellness policies. This study documented the strength and comprehensiveness of 1 state's written district policies using a coding tool, and tested whether these traits predicted school-level implementation and practices. Methods: School wellness policies from 151 Connecticut districts were evaluated. School principal surveys were collected before and after the writing and expected implementation of wellness policies. Sociodemographic variables were assessed for each district, including enrollment, population density, political climate, racial composition, and socioeconomic status. Changes in school-level policy implementation before and after the federal wellness policy mandate were compared across districts by wellness policy strength; policies were compared based on district-level demographics. Results: Statewide, more complete implementation of nutrition and physical activity policies at the school level was reported after adoption of written policies. Districts with stronger, more comprehensive policies were more successful in implementing them at the school level. Some sociodemographic characteristics predicted the strength of wellness policies. Conclusions: Written school wellness policies have the potential to promote significant improvements in the school environment. Future regulation of school wellness policies should focus on the importance of writing strong and comprehensive policies. (Contains 2 tables.)