Childhood obesity has been recognized as not only a personal disease, but also as a social problem inducing government development of policies to address the childhood obesity problem. Since the National School Lunch Program (NSLP) has been one of the most important nutrition supplement programs for children, the government has tried to solve the childhood obesity problem through the NSLP.We set a goal of the pa- per as investigating theoretical relationship between the NSLP and the children's BMI and establishing support for a new school lunch program policy emphasizing quality of foods to reduce the childhood obesity epidemic. To develop an e¢ cient nutrition sup- plement policy on the childhood obesity problem, this paper studies the significance of participation in the NSLP on the improvement in childhood obesity and clarifies conditions to encourage parents' continued participation in the NSLP using both the- oretical and empirical models. The theoretical results show that participating in the NSLP a¤ects the children's BMI change and contributes to improving the childhood obesity problem. Moreover, the results exhibit if the marginal rate of substitution be- tween high and low calories in the NSLP is greater than eating at home, the parent of an overweight child is more likely to continue participating in the NSLP to solve their childs obesity problem. The theoretical results are tested empirically by using the ECLS-K data and we simulate the childs BMI percentile change based on the empirical results.