"The NBER Bulletin on Aging and Health provides summaries of publications like this. You can sign up to receive the NBER Bulletin on Aging and Health by email. In this paper, we investigate the impact of attending school on body weight and obesity. We use school starting age cutoff dates to compare weight outcomes for similar age children with different years of school exposure. As is the case with academic outcomes, school exposure is related to unobserved determinants of weight outcomes because some families choose to have their child start school late (or early). If one does not account for this endogeneity, it appears that an additional year of school exposure results in a greater BMI and a higher probability of being overweight or obese. When actual exposure is instrumented with expected exposure based on school starting dates and birthday, the significant positive effects disappear, and most point estimates become negative and insignificant. However, for children not eating the school lunch, there is a significant negative effect on the probability of being overweight"--National Bureau of Economic Research web site.