This chapter describes a model for continuous improvement that guides the work of the National Center on Scaling Up Effective Schools, or NCSU. NCSU is a research and development center funded by the Institute for Education Sciences, the research arm of the United States Department of Education. At the core of the Center's work is an innovative process to bring to scale practices that have been shown to improve student achievement in high schools in Broward County, Florida, and Fort Worth, Texas. To do so, the Center's model of improvement relies on three core principles. First, a prototype is built to reflect the core elements of programs or practices that have been shown to be effective locally. Second, rapid-cycle testing is used to allow the prototype to be revised in ways that adapt it to a particular school context. Third, a researcher-practitioner partnership is employed that strives to both take advantage of and build local ownership and expertise. In so doing, the continuous improvement model addresses well-known challenges faced by those attempting to scale up educational innovations, challenges such as building teacher buy-in and attending to the organizational context in which innovations are to be enacted.