The "District of Columbia School Choice Incentive Act of 2003," passed by the Congress in January 2004, established the first federally funded, private school voucher program in the United States. The purpose of the new scholarship program was to provide low-income residents, particularly those whose children attend schools in need of improvement or corrective action under the "Elementary and Secondary Education Act," with "expanded opportunities to attend higher performing schools in the District of Columbia" (Sec. 303). As part of this legislation, the Congress mandated a rigorous evaluation of the impacts of the Program, now called the "DC Opportunity Scholarship Program" (OSP). This report presents findings from the evaluation on the impacts three years after families who applied were given the option to move from a public school to a participating private school of their choice. The evaluation is based on a randomized controlled trial design that compares the outcomes of eligible applicants randomly assigned to receive (treatment group) or not receive (control group) a scholarship through a series of lotteries. The main findings of the evaluation so far include: (1) After 3 years, there was a statistically significant positive impact on reading test scores, but not math test scores; (2) The OSP had a positive impact overall on parents' reports of school satisfaction and safety, but not on students' reports; (3) This same pattern of findings holds when the analysis is conducted to determine the impact of using a scholarship rather than being offered a scholarship; (4) The OSP improved reading achievement for 5 of the 10 subgroups examined; and (5) No achievement impacts were observed for five other subgroups of students, including those who entered the Program with relative academic disadvantage. Six appendices are included: (1) Research Methodology; (2) Benjamini-Hochberg Adjustments for Multiple Comparisons; (3) Sensitivity Testing; (4) Detailed ITT Tables; (5) Relationship Between Attending a Private School and Key Outcomes; and (6) Intermediate Outcome Measures.. (Contains 115 footnotes, 15 figures and 129 tables.) [For Executive Summary, see ED504784. For "Evaluation of the DC Opportunity Scholarship Program: Impacts after Two Years", see ED501696. For "Evaluation of the DC Opportunity Scholarship Program: Impacts after One Year", see ED497154.]