Edison Schools, Inc., is the largest and most visible among a growing number of Education Management Organizations that have entered into contracts to manage public schools, including both conventional and charter schools. Edison's approach to managing schools is comprehensive, and it distinguishes itself from most other school improvement strategies by simultaneously addressing both the resources and assistance provided to schools and the accountability systems under which school staff operate. In this article we explore the ways in which the assistance and resources provided by Edison (including diverse professional development opportunities, materials, technology, and other tools), as well as accountability mechanisms (such as monitoring and rewards), have translated into principal and teacher actions, and the factors that facilitated or constrained educators' efforts to implement the Edison design and improve teaching and learning. Drawing on data gathered from extensive interviews, observations, and document reviews collected during a four-year comprehensive study of Edison schools, we demonstrate how Edison intends to promote not only educators' capacity but also their motivation and opportunity to deliver high-quality instruction. We examine variation that occurs across schools as teachers and principals respond to these system-level efforts. In addition, we identify several important predictors of variation in implementation, including the strength of instructional leadership provided by the principal and the presence or absence of district-imposed constraints such as union contract rules.Portions of this article were drawn directly from a RAND report (see Gill et al., 2005). Correspondence should be sent to Julie Marsh, RAND,