To contain the initial spread of the SARS-CoV2 virus and the COVID-19 disease, many countries opted to close schools. However, the importance of schooling to mitigate inequalities motivated many economies to reopen schools after having formulated various COVID-19 mitigation and containment strategies. Using an exploratory sequential mixed method design, we explore the measures undertaken by countries when reopening schools and how these measures varied cross-nationally. We find that countries formulated a wide number (total: 242) and range of school reopening measures to mitigate the spread of the virus in the early months of the COVID-19 pandemic. From a policy diffusion theoretical perspective, findings from our statistical analyses suggest that cross-national diversity in policies is related to both internal and external country factors such as peer emulation mechanisms, income, and past pandemic experiences. We urge international agencies for more explicit guidelines for effective school reopening measures.