Prior research has shown positive associations between participation in school meals and some dietary measures, but the evidence is equivocal. Few prior studies have used methodological approaches that address underlying differences in food preferences and health beliefs between school meals participants and nonparticipants, resulting in the potential for selection bias to influence results. This study estimated relationships among school meals participation and weekday energy intake and dietary quality, controlling for weekend dietary intake as a proxy for food preferences and health beliefs. Further, this paper explored how family income moderated these relationships. NHANES data (2003-2008) were analyzed for children aged 6-17 y with reliable dietary recalls for one weekday and one weekend day (n = 2376). Using multivariate linear regression models, we examined weekday-weekend differences in energy intake as a percentage of the estimated energy requirement (%EER) and differences in Healthy Eating Index-2005 (HEI) scores for breakfast and lunch and for the entire day. Overall, school meals participants and nonparticipants had equivalent %EERs and total HEI scores, but participants scored higher for milk and lower for saturated fat and sodium after adjustment for weekend eating. Family income moderated the relationship between school meals participation and HEI. Low-income children who ate school breakfast and lunch had significantly higher total HEI, and total grain, and meat and beans component scores. Conversely, higher income participants had significantly lower scores for total grains, whole grains, and saturated fat. Changes to the content of school meals may differentially affect weekday dietary intake of low-income and higher income participants.