Aims To develop a theory describing the processes and actions involved with school nurse case management for school-aged children with chronic conditions in the K12 system. Design Case management is an essential practice for the school nurse. Little is known about actual case management practice in real-world settings. Grounded theory methodology following a literature-based conceptual model of school nurse case management. Methods A purposive maximum variation sampling was used for data collection and analysis. Semi-structured interviews conducted in-person and via conferencing software from January to March 2017 with school nurses practicing in Washington State until data saturation was achieved. A condition lasting at least 6 months was also used to define a chronic condition. Results In all, 14 school nurses with an average of 12 years of experience were interviewed. Analysis revealed that the core strategy used by participating nurses for case management involved navigating through ambiguity; balancing multiple roles; seeking guidance and training; acknowledging imperfect functioning and navigating poor system supports. Conclusion The findings suggest that actual school nurse case management practice differs from best practice recommendations. Participants did not discuss health promotion or environmental management and did not act to set goals or prioritize care as suggested in the literature. Impact This article informs nursing leadership of the real-world challenges faced by nurses performing case management in the school setting. These findings indicate that improvements in system supports and training, together with tolerance for the challenges nurses face in providing such care, might improve case management practice in the schools.