The impact of school-based Tae Kwon Do training on self-regulatory abilities was examined. A self-regulation framework including three domains (cognitive, affective, and physical) was presented. Children (N = 207) from kindergarten through Grade 5 were randomly assigned by homeroom class to either the intervention (martial arts) group or a comparison (traditional physical education) group. Outcomes were assessed using multidimensional, multimodal assessments. After a 3-month intervention, results indicated that the martial arts group demonstrated greater improvements than the comparison group in areas of cognitive self-regulation, affective self-regulation, prosocial behavior, classroom conduct, and performance on a mental math test. A significant Group x Gender interaction was found for cognitive self-regulation and classroom conduct, with boys showing greater improvements than girls. Possible explanations of this interaction as well as implications for components of martial arts training for the development of self-regulation in school-age children are discussed.