Objective: The objective of this study is to examine associations between aspects of the environment in school neighborhoods and childhood body mass index percentile (BMIp). Methods: Trained medical students visited 46 elementary schools in the Kansas City metropolitan area to conduct medical screenings that included the height and weight measurements of 12 118 boys and girls 4-12 years of age in the academic year 2008-2009. For the same time period, aspects of the built environment in a 2-mile radius around each school was obtained from the Walkscore database. Other environmental characteristics (for example, population change) of these areas were also obtained from various sources. Hierarchical linear modeling was used to estimate the associations between neighborhood- and individual-level factors and BMIp. Results: Population size along with the number of fast-food restaurants and grocery stores were positively associated with BMIp, whereas population change along with the number of parks and fitness centers were inversely associated with BMIp. Conclusions: After considering individual-level factors and the random effects of schools, environmental elements of school neighborhoods predict childhood BMIp. This study offers evidence of the health influence of school neighborhoods in a way that can inform neighborhood redevelopment efforts. © 2014 Macmillan Publishers Limited.