This book presents a story of school improvement activity in East Africa from 1985 to 2000, which focused on sustained teacher development. The core of the book consists of six evaluations of school-and district-wide school improvement projects (SIPs) supported by the Aga Khan Foundation in Tanzania, Kenya, and Uganda. The case studies present an evolving body of knowledge about the successes and challenges of a comprehensive approach to school improvement grounded in a common set of strategic principles. The strategic principles embody the belief that the chances for quality improvement in teaching and learning are greater when change efforts *are school-based, *involve whole schools as the unit of change, *emphasize the ongoing professional development of teachers, *attend to school management and organizational conditions affecting the capacity of teachers to implement change, * prepare for the institutionalization of organizational structures and processes that enable continuous school development, and *evolve through partnerships among relevant education stakeholders. The book concludes with commentaries by international experts in school improvement and teacher development on the SIP project designs, implementation and outcomes, and on lessons that can be drawn from the projects and their evaluations for school improvement policy, practice and theory in developing and developed countries around the world.