This study assessed the effects of afterschool program participation on academic achievement of middle school students, using data from the Korean Education Longitudinal Study. A propensity score matching approach was employed to control for preexisting differences between students who participated in an afterschool program and those who did not. Results showed that afterschool program participation had a negative effect on academic achievement for the general student population. However, afterschool program participation was found to have a positive effect on academic achievement in Korean language and English for students from small towns and rural areas even after controlling for the other variables. These findings suggest that afterschool program participation plays a significant role in reducing the regional achievement gap. The authors highlighted several unique features of afterschool program participation in small towns and rural areas, which may explain the positive effect for students in these areas.