Peer Effects of Obesity on Child Body Composition

This study investigates whether peer obesity is a driver of individual weight changes in public school children and whether the impact of peer effects changes as children age. Quantifying peer effects is important for understanding the social determinants of obesity and for planning effective school wellness policies. However, the extant empirical research on peer effects is limited due to difficulties in separating causal influences from confounding factors. This study overcomes some of these difficulties by using a within-school, across-cohort empirical design to separate confounding factors at the individual, school and school-grade level for over one million public school children in New York City followed over a decade. The results show that increases in both (a) the proportion of obese classmates and (b) average classmate Body Mass Index (BMI) lead to modest but meaningful increases in a child's own BMI. Peer-effects decline steadily as children age. These findings suggest that the critical time for school-grade level intervention may be in the earliest ages of childhood development.