During this pandemic, does that harm to student’s learning, and the isolation-induced mental harm, outweigh the risk—to children, school staff, families, and the community at large—of keeping schools open and giving the coronavirus more chances to spread? Gretchen Vogel writes in Science that the one country that could have definitively answered that question has apparently failed to collect any data. Bucking a global trend, Sweden has kept day care centers and schools through ninth grade open since COVID-19 emerged, without any major adjustments to class size, lunch policies, or recess rules. That made the country a perfect natural experiment about schools’ role in viral spread that many others could have learned from as they reopen schools or ponder when to do so. Yet Swedish officials have not tracked infections among school children—even when large outbreaks led to the closure of individual schools or staff members died of the disease.