NEW DIRECTIONS FOR YOUTH DEVELOPMENT, NO. 114, SUMMER 2007 © WILEY PERIODICALS, INC. Published online in Wiley InterScience (www.interscience.wiley.com) • DOI: 10.1002/yd.211 33 Children are more vulnerable to gaining body mass index during the summer than during the school year, suggesting that schools help to reduce childhood obesity. 2 Childhood body mass index gain during the summer versus during the school year Douglas B. Downey, Heather R. Boughton BY NOW IT IS WELL KNOWN that obesity has been increasing in the United States. Whereas this health problem has affected nearly every segment of the population, the impact on children, in whom the incidence of obesity has tripled in the last twenty years, is of special note. 1 Overweight children tend to become overweight adults, more vulnerable to the wide range of health problems asso- ciated with obesity. The role that schools play in this problem is difficult to discern, however, because children’s health is affected by both school and nonschool factors. In this chapter, we discuss innovative research that compares children’s body mass index (BMI) gains in the summer versus the school year. Although many scholars, and certainly the popular media, currently focus on school-based solutions to childhood obesity, this research suggests that when it comes to children’s BMI gain, schools are more a part of the solution than the problem. Specifically, children gain BMI roughly twice as fast during the summer as during the school year.