Using data from the third School Nutrition Dietary Assessment Study (SNDA-III), this study assessed the quality of school-age children’s overall diets and the relationship to school meal participation, using a version of the Healthy Eating Index (HEI)-2005 adapted to use with a school-age population. Propensity score matching techniques were used to control for observed characteristics of school meal participants and nonparticipants. Overall, school meal participants and nonparticipants had diets of similar quality, although school meal participation was associated with better Milk Group intakes and lower intakes of Healthy Oils. Diets of both groups had substantial room for improvement. This study was conducted by Mathematica Policy Research, Inc., under a cooperative research contract with USDA’s Economic Research Service (ERS)Food and Nutrition Assistance Research Program (FANRP): contract number 59-5000-7-0110 (ERS project representative: Joanne Guthrie). The views expressed are those of the authors and not necessarily those of ERS or USDA.