In school systems around the world, there is an increasing focus on students’ academic achievement. The challenge of how to improve schools is an important issue for all levels in the school system. However, a central question of both practical and theoretical relevance is how it is possible to understand why (or why not) school-development efforts are successful. The purpose of this article is to explore the ecology of local school development through the case of a medium-sized municipality in Sweden, based on empirical data from two follow-up research projects. The analytical framework draws from organisational theory and new institutional theory, where focus is directed towards how different sub-systems of the school organisation interact with and respond to aspects of development work and the implications for outcomes of school-development initiatives. Findings show that great investment of resources from the central level in the local school organisation necessarily does not lead to changes in teaching practice. School-development initiatives are unlikely to be successful unless they engage and re-couple the involved sub-systems. Finally, we discuss how the introduction of Expert Teachers as a new sub-system has the ability to work as a link between other sub-systems and to promote school development.