Most countries introduced school closures during the spring of 2020 despite substantial uncertainty regarding the effectiveness in containing SARS-CoV-2. In Sweden, upper-secondary schools moved online while lower-secondary schools remained open. A comparison of parents with children in the final year of lower-secondary and first year of upper-secondary school shows that keeping the former open had limited consequences for the overall transmission of the virus. However, the infection rate doubled among lower-secondary teachers relative to upper-secondary ones. The infection rate among partners of lower-secondary teacher was 30 percent higher than among their upper-secondary counterparts.