The Kauffman School is a public charter school that serves students from low-income neighborhoods in Kansas City, Missouri. This paper used a matched comparison group design to estimate the impacts of the Kauffman School on student achievement, attendance, and suspensions. We found that the Kauffman School had positive and statistically significant impacts on student achievement in mathematics, reading, and science. This paper also used surveys, interviews, focus groups, and classroom observations to describe the hallmarks and operations of the Kauffman School and explore possible mechanisms for its effects, informing the literature on school effectiveness. We found evidence that the Kauffman School's hallmarks are largely being implemented faithfully, and that key stakeholders believe the Kauffman School's methods are having a positive influence on students' behavior, attitudes, and performance.