To curb the spread of the coronavirus, almost all countries implemented nationwide school closures. Suddenly, students experienced a serious disruption to their school and social lives. In this article, we argue that psychological research offers crucial insights for guiding policy about school closures during crises. To this end, we review the existing literature on the impact of school closures during the COVID-19 pandemic on children's learning and mental health. We find that the unprecedented scale and length of school closures resulted in a substantial deficit in children's learning and a deterioration in children's mental health. We then provide policy recommendations on how to ensure children's learning and psychosocial development in the future. Specifically, we recommend that more attention should be paid to students from marginalized groups who are most in need of intervention, evidence-informed and personality-tailored mental-health and social- and emotional-learning programs should be implemented in schools, and generational labels should be avoided.