Networking and collaboration between schools have become increasingly popular approaches to school improvement in recent years. This move is seen to arise from advances in the understanding of learning and especially the perceived advantages of collaborative learning, an increased need for innovation stemming from intensified external pressure and rapid changes to school environments, and the perceived shortcomings of school improvement based on single schools or external support and pressure. While this evolution has triggered research on individual collaborative programmes and on factors which can enhance or act as barriers to collaboration, this research has been largely a-theoretical. In this study we will try to plug this gap by looking at four theoretical approaches underlying the broader concept of network theory: constructivist organizational theory, the theory of social capital, the theory of New Social Movements and Durkheimian network theory. We will discuss the application of these theories to educational collaborations and networks, both with reference to existing studies through a review of the literature and through further empirical research using six case studies of school networks in England, designed to represent different forms of networking in terms of factors such as the extent to which the collaboration is coercive as opposed to voluntary, the size of the network and the goals of the network. We will discuss the applicability of these theories to practice and lessons that can be learnt for future collaboration and the leadership thereof.