The study of people's social ties, the resources they obtain from them, and the communication tools--such as the Internet--that facilitate the flow of expertise and resources makes up an evolving science of networks that can help school leaders better understand how to support and promote school change. The science of networks is not new in itself, but its application to the functioning of schools is. More recently, researchers have begun to use social network analysis to analyze school leadership, teacher communities, and the diffusion of innovations in schools. It turns out that--as in other domains--networks matter for school change. In teacher networks--the focus of this article and the research presented here--the kinds of information and resources that circulate include: (1) ideas about teaching, learning, and assessment; (2) discussions coordinating different school activities; (3) stories of students including their successes and difficulties; (4) strategies for managing learning in groups; (5) tips for efficient use of technology; and (6) views on administrators and administration. Some of this information is potentially of great use in facilitating school change, such as when a teacher shares an idea about use of a particular strategy for teaching writing in the classroom or demonstrates a method of assessment for a colleague. To promote effective teacher collaboration, school leaders must examine all the social networks already in place and ensure that expertise and other social resources are available at multiple levels in the school community. Some of the key findings from the study that may be of use to school leaders are also presented. (Contains 13 notes.)