During the last four decades, educational researchers and practitioners have intensively engaged in bringing about positive changes in schools. Therefore, the kinds of changes introduced to schools have become complex in nature and overwhelming in number--from improving teacher professional knowledge base and teaching repertoires to developing innovative curricula to changing the organizational structures and cultures in schools. The skills required by schools and teachers to implement these changes have also become more complex. Consequently, a large number of external agents--variously referred to as consultants, linking agents, education officers, or supervisors--have mobilized themselves for building schools' capacity and knowledge utilization at the local level. This article intends to analyse the existing stock of knowledge and understanding about external agents' roles and practices in school change, focusing on the significance, limitations, diversity and magnitude, and the challenges and tensions attached to this role in both developed and developing nations. The comparative analysis of the external change agents' roles and practices in the developed and developing country contexts provides useful insights into how context influences the change agents' roles and practices in school change. (Contains 2 tables and 1 note.)