This dissertation studies the short-term effects of attending an after-school program (i.e., LA's BEST) on student mathematic achievement. The effects of one, two and three years of participation are studied, as well as the extent to which the magnitude of these effects varies across grades in which participation occurs, and the extent to which they may be moderated by student or school characteristics. The dissertation rises longitudinal data for 2001-2005, a within-schools design, propensity score matching, and two distinct control groups to estimate the participation effects. Results of this study are mixed. Overall positive but small one-year participation effects are observed, and various interaction effects are found between treatment and parental education, English language proficiency of the student, and gender. Results for two years of participation are less consistent and no participation effects are found for three years of participation. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]