In the aftermath of the COVID-19 pandemic, there is greater recognition of the important aim of strengthening the robustness of service systems. As an aim of some purpose-oriented networks (PONs) is to strengthen service systems, we argue robustness should be considered as an outcome for these cross-organizational collaborative efforts in public administration. Thus, the question motivating our research is how collective efforts, like PONs, can improve the robustness of a system? Specifically, our research is guided by the questions of which structural factors may be key to achieving system robustness and how does a PON strengthen the system to achieve those structural characteristics? Drawing on a longitudinal mixed methods study of a child education and development (CED) network, we examine the change in the CED system structure from dependence on a few hub organizations, and the inherent vulnerabilities of that structure, to one with a large core and less likely to fragment. We then analyze how redundancy and diversity of the core increases the robustness of the system. Last, we identify the PON processes that lead to these core characteristics. We use our findings to offer implications for theory and practice on how PONs can strengthen the robustness of service systems.