The Kauffman School is a public charter school serving 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 large positive impacts on student achievement in mathematics, reading, and science. This paper also used qualitative data to explore possible mechanisms for the school's effects. We found evidence that the Kauffman School's hallmarks are being implemented faithfully, and that stakeholders believe the school's methods are having a positive influence on students' attitudes and performance