Is being in school better? The impact of school on children's BMI when starting age is endogenous.

In this paper, we investigate the impact of attending school on body weight and obesity using a regression-discontinuity design. 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 we compare the weight outcomes of similar age children with one versus two years of school exposure due to regulations on school starting age, the significant positive effects disappear, and most point estimates become negative, but insignificant. However, additional school exposure appears to improve weight outcomes of children for whom the transition to elementary school represents a more dramatic change in environment (those who spent less time in childcare prior to kindergarten).