In the 2007-2008 school year, the New York City Department of Education and the United Federation of Teachers jointly implemented the Schoolwide Performance Bonus Program in a random sample of the city's high-needs public schools. The program lasted for three school years, and its broad objective was to improve student performance through school-based financial incentives. The question, of course, was whether it was doing so. To examine its implementation and effects, the department tasked a RAND Corporation-led partnership with the National Center on Performance Incentives at Vanderbilt University to conduct a two-year study of the program that would offer an independent assessment. This report describes the results of our analyses for all three years of the program, from 2007-2008 through 2009-2010. This work built on past research and was guided by a theory of action articulated by program leaders. Researchers examined student test scores; teacher, school staff, and administrator surveys; and interviews with administrators, staff members, program sponsors, and union and district officials. The researchers found that the program did not, by itself, improve student achievement, perhaps in part because conditions needed to motivate staff were not achieved (e.g., understanding, buy-in for the bonus criteria) and because of the high level of accountability pressure all the schools already faced. Individual chapters contain footnotes. (Contains 12 figures and 66 tables.) [Additional funding for this paper was provided by the New York City Fund for Public Schools. For "What New York City's Experiment with Schoolwide Performance Bonuses Tells Us about Pay for Performance. Research Brief," see ED521918.]