Purpose: Replicating and extending earlier research, this mixed-methods study inquired about the characteristics of effective school leadership networks and the contribution of such networks to the development of individual and collective leaders' professional capacities. Design: The study used path analytic techniques with survey data provided by 283 school and district leaders to test a path model of effective network characteristics. Interview data were provided by 23 school leaders. Variables in the model included Network leadership, structure, health, connectivity, and outcomes. Findings: Results confirmed that the model was a very good fit with the data and, as a whole, explained 51% of the variation in network outcomes. Network leadership had the largest total effect on network outcomes, followed closely by the effects of Network Health and Network Connectivity. Interview data confirmed the nature of variables measured by the survey and added additional features for future research. Most results replicated the previous study. Research Limitation: The study was limited to leadership networks intentionally organised within districts, not networks organised by school leaders themselves or networks arising spontaneously by their members. Results cannot be generalised to other types of networks. Practical implication: 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: 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.