The substantial increase in the prevalence of child obesity over recent decades and its association with a number of negative health and economic outcomes suggests its strong potential as an influence on the lifecourse development of health and productivity. This paper evaluates interactive effects between family socioeconomic status (SES) and height on child obesity in the United States. Using the 1999-2006 National Health and Nutrition Examination Surveys (NHANES), the results of this paper confirm previous findings that taller children exhibit greater propensity towards obesity as measured by body mass index (BMI) and that obesity is inversely related to family SES as measured by poverty status. The analysis adds to the existing literature by showing that the magnitude of the SES-obesity association is larger in taller children. Age and sex patterns are evaluated that suggest the SES-height interaction persists through childhood and adolescence in males but is only evident in females during adolescence. Interaction effects are also shown to be most evident in white males and Hispanic females. Policy implications are discussed and directions for future work are suggested.