A growing body of evidence indicates that the test scores of low-income children drop significantly relative to their higher-income counterparts during the summer months. This study finds that a well-implemented summer learning program can improve reading skills and increase the extent to which parents encourage their children to read during the subsequent school year. These findings provide some support for investments in out-of-school time programming for low-income children during the summer, such as those currently coming from the 21st Century Community Learning Centers program and the Supplemental Services provisions of Title I of the "No Child Left Behind" Act. This study used random assignment, the gold standard of evaluation methods, to evaluate the effectiveness of the Building Educated Leaders for Life (BELL) program--a summer program designed to improve academic skills, parental involvement, academic self-perceptions, and social behaviors among low-income children and families. Over 1,000 elementary school children who applied to BELL summer programs in New York and Boston in 2005 were randomly chosen to be in either a treatment group that was selected to participate in the BELL summer program, or a comparison group that was not. Independent researchers collected student reading tests (Gates-MacGinitie) and student and teacher surveys. The study found that children in the BELL treatment group gained about a month's worth of reading skills more than their counterparts in the comparison group during the summer. This is a modest, yet notable increase in reading skills for a six-week program. The study also found evidence of positive impacts on the degree to which parents encouraged their children to read. No impacts were found on academic-self perceptions or social behaviors. Overall, this study provides scientifically rigorous evidence regarding the ability of the BELL summer program to improve the reading skills of low-performing elementary school children. Few out-of-school time programs have produced evidence of effectiveness when evaluated in such a rigorous manner. The results are of particular importance given the longstanding public policy focus on raising achievement levels of low-income students. The following are appended: (1) Changes from Original Analysis Plans; (2) Adjusting for Time in School before Test; (3) Robustness Tests; (4) Supplementary Tables; and (5) BELL 2005 Parent Survey. (Contains 14 tables.)