This CPRE report is a reprint of a chapter that originally appeared as Chapter 49 of the Handbook of Education Policy Research, edited by Gary Sykes, Barbara Schneider, and DavidN.Plank and published for theAmerican Educational Research Association by Routledge Publishers in 2009. The reprinted chapter presents key findings from A Study of Instructional Improvement, a study that was conducted under the auspices of the Consortium for Policy Research in Education and directed by Brian Rowan, David K. Cohen, and Deborah Loewenberg Ball (all at the University of Michigan).This study examined the design, implementation, and instructional effectiveness of three of America’s most widely disseminated comprehensive school reform programs (the Accelerated Schools Project,America’s Choice, and Successful forAll) over a four year period that encompassed the school years 2000–2001 through 2003–2004. During the course of the study, data were collected in 115 elementary schools in every region of the United States,with more than 5,300 teachers, 800 school leaders, and 7,500 students and their families participating.