This paper employs a novel identification strategy based on changes in the route students would use to commute between their home and their school as they transition to higher grades housed in different schools to investigate the effect of fast-food availability on childhood weight outcomes by gender, race and location. Using a longitudinal census of height and weight for public school students in Arkansas, we find no evidence that changes in fast-food exposure are associated with changes in BMI z-score. Our findings suggest that laws restricting fast-food restaurants from areas near schools are neither effective nor efficient means of improving public health.