This study examined the effectiveness of a supervised mentoring program designed to improve the academic achievement of 834 low-income elementary and secondary school students in Seoul, South Korea. When compared to the control group, both elementary and middle school students exposed to the mentoring program improved in mathematic and reading comprehension, with an effect size 0.29 and 0.33 respectively. Additionally, the duration of the mentoring relationship affected the achievement of participating students. These findings provide support for mentoring programs as a means to reduce resource inequity in low-income school districts and, in so doing, contribute to higher levels of achievement. (Contains 4 tables.)