Proposing an integrative framework that links Bryk and colleagues’ five essential supports for school improvement and Porter and colleagues’ policy attribute theory, I use a mixed-methods approach to study the implementation and effectiveness of school turnaround efforts in the School District of Philadelphia. Using a matched comparison design and estimating a series of regression models to analyze data from Philadelphia’s central school improvement models as well as a group of comparison schools, I explore the relationships among key model components, approaches to implementing these components, and academic achievement. The use of an integrative framework for school improvement facilitates the unpacking of the idea of “success” in school reform, and careful examination of key reform components and implementation strategies provides insights into why particular school improvement models are (or are not) associated with gains in academic achievement. Qualitative methods are used to contextualize these findings and offer hypotheses to explain variation in essential supports, policy attributes, and achievement outcomes. This study facilitates the development of an empirically grounded theory of how implementation relates to effectiveness that proves useful in evaluating school turnaround, and in assessing how policymakers and implementers might leverage various aspects of implementation to create effective school improvement models at scale. Ultimately this study finds that how improvement models are implemented is more important than what key components models use in terms of explaining improvements in student achievement.