It is well known that good eating habits are important for growth and health. One must record the diet and analyze the nutrients to assess whether one’s eating habits are good. However, it is difficult for general people, including school students. Thus, a simple and easy method has been developed to evaluate the diets: an empirical dietary inflammatory index (DII). DII is a relatively simple diet evaluation method based on foods' anti- or pro-inflammatory effects. High DII diets enhance inflammation and increase the risk of chronic diseases, but low DII diets suppress inflammation and lower the risk. The evidence of the usefulness of DII has been accumulated, and it would be a good tool to reflect one’s eating habits. In this study, we evaluated the efficacy of DII for high school students in healthy eating habits education. There are some significant associations in concentration/decision making in males and view of myself in females, respectively, between the lower DII group and the higher DII group. Many students recognized DII as a simple and easy method to evaluate their diets compared to conventional methods. These results suggest that DII is a potent method for reflection on diet habits, and learning it in high school could contribute to students’ lifelong health.