We conducted an examination of quality control for five school lunch meals offered in June and November. The differences in weight and nutrient content between the time of menu planning and the time the meals were served were measured as yield and nutrient retention factors, respectively. The yield factor was derived from the ratio of the weight of the total ingredients at the time of menu planning to the weight of the school lunch meal served. The yield factors for the five school lunch meals ranged between 87% and 94%, revealing a loss during the preparation process. Furthermore, seasonal ingredients were found to affect the yield factor of dishes using such ingredients. The nutrient retention factor was obtained by measuring the ratio of the nutrient content value of total ingredients at the time of menu planning to the value of the content analysis of school lunch at the time of serving. In all five school lunch meals, a significant decline in the nutrient retention factors was observed for energy content, calcium, magnesium and zinc. Furthermore, significant increases in vitamin A and dietary fiber were observed. However, no differences were observed for protein, fat, carbohydrates, sodium, iron, vitamin B1, vitamin B2, and vitamin C. as the intake amounted to 95% of the weight of the food served and the nutrient intake exceeded 95% for most nutrients except vitamins A and C, the school meals were found to be of high quality,. The quality evaluation of school lunch based upon the yield and nutrient retention factors revealed the need for identifying and investigating the causes of loss or gain during the preparation process to achieve quality improvements.