We offer a comparative analysis of public and private schools, presenting data from a new national study—the Administrator and Teacher Survey—that expands on the pathbreaking High School and Beyond survey. We find that public and private schools are distinctively different in environment and organization. Most importantly, private schools are more likely to possess the characteristics widely believed to produce effectiveness. We argue throughout that the differences across the sectors are anchored in the logic of politics and markets. This argument derives from our belief that environmental context has pervasive consequences for the organization and operation of all schools and specifically that the key differences between public and private environments—and thus between public and private schools—derive from their characteristic methods of social control: the public schools are subordinates in a hierarchic system of democratic politics, whereas private schools are largely autonomous actors “controlled” by the market.