The Heart and Stroke Foundation's Spark Together for Healthy Kids™ (Spark) is a multiyear initiative in Ontario, Canada, that takes a population approach to obesity prevention. It focuses on creating healthy environments by improving access to healthy foods and physical activity, with an emphasis on strengthening the advocacy capacity of organizations and citizens. Consistent with the complexity of the intervention, the evaluation of Spark applied systems concepts and methods to test the utility of network analysis as a method for evaluation, and to inform collaborations of organizations involved in programs and advocacy. Relationships among organizations from different sectors and jurisdictional levels with a focus on school community environments were of particular interest. Interorganizational network analysis was used to understand these relationships, including the role of the Heart and Stroke Foundation. Findings revealed a niche brokering role for the Heart and Stroke Foundation and other provincial and national organizations, and the importance of these brokers for engaging local and regional organizations. Findings also reinforced the importance of a mixed methods approach to network analysis, and the potential value of the analysis for scientific and practical purposes.