Despite prestigious reports, most notably "A Nation at Risk," and fervent reform efforts, school performance is unlikely to be improved by measures failing to recognize that schools are institutions--complex organizations composed of interdependent parts, governed by well-established rules and norms, and adapted for stability. Effective schools cannot flourish unless superintendents, school boards, and other outside authorities delegate meaningful control over school policy, personnel, and practice to the schools themselves. High school performance gains will require basic changes in school governance and organization--changes threatening the security of political representatives and administrators heavily invested in the existing system. This study developed a comprehensive database to explore these issues. The database supplements a national survey and testing of 25,000 students in 1,000 public and private high schools (the High School and Beyond Study) with a survey of teachers and principals in a representative sample of half the schools. This supplement, the Administrator and Teacher Survey, was designed to measure elements of school organization related to school effectiveness. High- and low-performance schools were found to differ dramatically in their student bodies and informal organization. Students from high-performance schools were typically Caucasian and from well-educated, affluent families. Leadership was stronger in high-achievement schools; staff shared a commitment to academic excellence and worked as a team to create a more productive learning environment. A multiple regression technique proved that school organization significantly affected learning. The closing discussion explores ways to free schools from governmental and other controls. (MLH)