In this paper, we investigate the association between weight and children's educational achievement, as measured by scores on Peabody Individual Achievement Tests in math and reading, and grade attainment. Data for the study came from the 1979 cohort of the National Longitudinal Survey of Youth (NLSY), which contains a large, national sample of children between the ages of 5 and 12 between 1986 and 2004. We obtained estimates of the association between weight and achievement using several regression model specifications that controlled for a variety of observed characteristics of the child and his or her mother, and time-invariant characteristics of the child. Our results suggest that, in general, children who are overweight or obese have achievement test scores that are about the same as children with average weight. (Contains 5 tables.)