The District of Columbia School Choice Incentive Act of 2003, passed by Congress in January 2004, established the first federally funded, private school voucher program in the United States. Since that time, more than 8,400 students have applied for what is now called the DC Opportunity Scholarship Program (OSP), and a rigorous evaluation of the Program, mandated by Congress, has been underway. This last formal report from the ongoing evaluation describes the impacts of the Program at least four years after families who applied and were given the option to move from a public school to a participating private school of their choice. The research priorities for the evaluation were shaped largely by the primary topics of interest specified in the statute. This legislative mandate led the evaluators to focus on the following research questions: (1) What is the impact of the Program on student academic achievement? (2) What is the impact of the Program on other student measures? (3) What effect does the Program have on school safety and satisfaction? (4) What is the effect of attending private versus public schools? (5) To what extent is the Program influencing public schools and expanding choice options for parents in Washington, DC? These research questions are consistent with the topics that scholars and policymakers have identified as important questions of interest surrounding private school scholarship programs. The report found that that the Program had mixed longer-term effects on participating students and their parents, including: (1) No conclusive evidence that the OSP affected student achievement overall, or for the high-priority group of students who applied from "schools in need of improvement"; (2) The Program significantly improved students' chances of graduating from high school, according to parent reports. Overall, 82 percent of students offered scholarships received a high school diploma, compared to 70 percent of those who applied but were not offered scholarships. This graduation rate improvement also held for the subgroup of OSP students who came from "schools in need of improvement."; and (3) Although parents had higher satisfaction and rated schools as safer if their child was offered or used an OSP scholarship, students reported similar ratings for satisfaction and safety regardless of whether they were offered or used a scholarship. Appendices include: (1) Research Methodology; (2) Benjamini-Hochberg Adjustments for Multiple Comparisons; (3) Sensitivity Testing; (4) Relationship Between Attending a Private School and Key Outcomes; (5) Detailed ITT Tables; (6) Exploration of Whether Parents Get What They Seek From School Choice; (7) To What Extent Are Treatment Effects of the OSP Observed Across the Outcome Test-Score Distribution? Quantile Regression Analysis of the OSP; and (8) Intermediate Outcome Measures. (Contains 99 tables, 31 figures, and 61 footnotes.)