Background: Little is known regarding utilization of school-based health centers (SBHCs) during prolonged school closures, such as those that occurred during the COVID-19 pandemic. We sought to compare SBHC utilization before and after pandemic-related school closures across a network of SBHCs affiliated with a large Southern Californian urban school district. Methods: We conducted a secondary analysis of encounter data extracted from electronic health records from 12 SBHCs that remained open despite school closures, including patient demographics and diagnostic and billing codes. We used the Clinical Classifications Software Refined to group encounters for common primary care conditions. Utilization before and during pandemic-related school closures was compared using logistic regression with cluster-robust standard errors to account for clustering within clinics, after adjusting for month of encounter. Results: During the pandemic, study SBHCs conducted 52,530 encounters and maintained [approximately]4040 encounters/month. The frequency of encounters for annual preventative health exams increased for school-aged patients but decreased for other age groups while the frequency of encounters for mental health problems increased for all age groups. Implications for School Health Policy, Practice, and Equity: Despite pandemic-related school closures, SBHCs appeared play a critical role in providing primary care to vulnerable communities. Conclusions: SBHCs may hold value beyond their co-location with academic instruction.