Background: Income disparities in US youth in academic achievement appear to widen during the summer because of discontinued learning among children from lower-income households. Little is known about whether behavioral risk factors for childhood obesity, such as diet and physical activity, also demonstrate a widening difference by income when children are out of school. Methods: Data from US children in grades 1-12 in the National Health and Nutrition Examination Survey 2003-2008 (N = 6796) were used to estimate screen time, moderate-to-vigorous physical activity (MVPA), and consumption of calories, vegetables, and added sugar. Linear regression was used to compare among children of households =185% and >185% poverty, as well as during the school year versus on school breaks. Results: Children surveyed during summer breaks consumed fewer vegetables (-0.2 cups/day) and more added sugar (+2.1 teaspoons/day), were more active (+4.6 MVPA minutes/day) and watched more television (+18 minutes/day). However, the nonsignificant interaction between school breaks and income indicated that lower-income students were not "less healthy" than higher-income students during the summer breaks. Conclusion: Obesity-related risk factors were more prevalent during the summer and among lower-income youths, but the income disparity in these behaviors was not exacerbated when schools are not in session.