School closures are an important public health intervention during epidemics. Yet, the existing estimates of policy costs and benefits overlook the impact of human behavior and labor market conditions. We use an integrated assessment framework to quantify the public health benefits and the economic costs of school closures based on activity patterns derived from the American Time-Use Survey (ATUS) for a pandemic like COVID-19. We develop a policy decision framework based on marginal benefits and costs to estimate the optimal school closure duration. The results suggest that the optimal school closure depends on how people reallocate their time when schools are closed. Widespread social distancing behavior implemented early and for a long duration can delay the epidemic for years, buying time for the development of pharmaceutical interventions and yielding substantial net benefits. Conversely, school closure, with behavior targeted to adjust only to the school closure, is unlikely to provide substantial delay or sufficient net benefits to justify closing schools for pathogen control.