Purpose: The purpose of this paper is to inquire about the characteristics of effective school leadership networks and the contribution of such networks to the development of individual leaders' professional capacities. Design/methodology/approach: The study used path-analytic techniques with survey data provided by 450 school and district leaders in Ontario to test a path model of effective network characteristics. Variables in the model included network leadership, structure, health, connectivity, outcomes and unintended challenges. Findings Results confirmed that the model was a very good fit with the data, and as a whole, explained 51 percent of the variation in network outcomes. Network leadership had the largest total effect on network outcomes (R[superscript 2] = 0.56), followed closely by the effects of network health (R[superscript 2] = 0.49) and network connectivity (R[superscript 2] = 0.46). Research limitations/implications The study was limited to leadership networks intentionally organized within districts, not networks organized by school leaders themselves or networks arising spontaneously by their members. Results cannot be generalized to other types of networks. Practical implications In addition to a focus on single unit leadership development in districts, systematic initiatives should be designed to help prepare network leaders to foster the forms of collaboration that are so central to professional capacity development. Originality/value: Results of the study offer explicit guidance to network leaders about how to improve the contribution of network participation to their colleagues' capacities; it is one of a very small number studies in educational contexts to provide such guidance.