Attention deficit hyperactivity disorder (ADHD) is a common psychiatric disorder in school-age children and adolescents. However, the reported associations between ADHD and single nutrient intake are inconsistent. The aim of the study was to investigate the relationships between dietary intake changes and the prevalence of ADHD over time with repeat measurements using data from the Children Health and Environment Research (CHEER). To assess changes over time, we used data obtained in 2006 and 2008 (Phases and ). In this study, there were 2899 children aged 8 years or older in Phase and 2120 children aged 9 years or older in Phase from Korea, and the ADHD scores and dietary intake of 1733 children in Phases and were used in the final analysis. The YN group refers to children whose disease had improved in Phase , and the NY group refers to children diagnosed with ADHD in Phase . A notable within-group result was the increase in vegetable protein ( = 0.03) in the YN group. A between-group comparison showed that significant changes in nutrient intake could be confirmed most in the NY group, and the YN group tended to have a lower nutrient intake than the NY group. In the correlation of changes in nutrient intake and three subtypes (combined, AD, and HD), the total fat ( = 0.048) and animal protein ( = 0.099) showed a positive correlation with the prevalence of AD. Vegetable iron ( = 0.061 and = 0.044, respectively), zinc ( = 0.022 and = 0.007, respectively), vegetable protein ( = 0.074), and calcium ( = 0.057) had inhibitory effects on ADHD and its subtype. In conclusion, management of dietary and nutritional status should be considered to ameliorate ADHD and its subtypes in school-age children, and these relationships require further exploration in other settings.