This paper discusses how accountability pressures for schools to improve test score outcomes implemented under No Child Left Behind (NCLB) may affect children’s obesity. Using a unique dataset of Arkansas schools that merged school-level information on test scores, obesity, and other demographic information, researchers found that NCLB accountability rules may have unintended negative consequences for children’s weight. Schools on the margin of passing the Adequate Yearly Progress threshold under NCLB had approximately a 0.5 percentage point higher rate of overweight the following year. Follow-up survey data from school principals indicated that reductions in physical activity and worsening of the food environment may have been potential changes schools made in response to NCLB.