Since the mid-1980s there has been considerable interest in school improvement and school effectiveness among researchers, policy- makers and practitioners. The purpose of this article is to examine the core beliefs and the bases of knowledge produced by researchers in the field of school improvement. An attempt is made to organize the field by looking in turn at: 1. The history of the study of changes and school improvements; 2. The centralization and decentralization paradox; 3. The definitions of school improvement; 4. The process of school improvement; 5. A framework for school improvement and it's influential factors; 6. Common strategies used in school improvement; 7. The theoretical implications for school improvement.