Purpose: This article presents the conceptual framework, methodological design, and key research findings from a Spencer Foundation-funded project of long-term educational change over time. Research Design: Based on more than 200 interviews, supplementary observations, and extensive archival data, it examines perceptions and experiences of educational change in eight high schools in the United States and Canada among teachers and administrators who worked in the schools in the 1970s, 1980s, and 1990s. Findings: The article indicates that most mainstream educational change theory and practice in the field of educational administration neglects the political, historical, and longitudinal aspects of change to their detriment. Educational change, it finds, is shaped by the convergence of large-scale economic and demographic shifts that produce five change forces (waves of reform, changing student demographics, teacher generations, leadership succession, and school interrelations) that have defined three distinct periods of educational change during the past 30 years. Conclusions: These forces and their convergence have ultimately reaffirmed the traditional identities and practices of conventional high schools and pulled innovative ones back toward the traditional norm in an age of standardization (though to a lesser extent where the schools are professional learning communities or have anactivist orientation). Conclusions are drawn in the form of a strategic theory of sustainable change.