The purpose of this study was to determine the relationship between extracurricular activities and self-regulation in 400 five year old twin children. Extracurricular activities were assessed using the Health and Behavior Questionnaire, and self-regulation was assessed using the Children's Behavior Questionnaire. While there initially was a significant correlation between extracurricular activities and self-regulation, that correlation became non-significant when controlling for SES and sex in a mixed model regression model. Nearly all of the children who did not participate in extracurricular activities came from lower SES families, leading to a lack of a "control group" for the high SES families. When only taking into account the lower SES half of the sample, the correlation between extracurricular activities and self-regulation became stronger and the correlation between SES and self-regulation became non-significant. Extracurricular activities do appear to promote self-regulation in children coming from low SES families, yet their effects on children coming from high SES families is still unknown.