The broad and substantial educational harm caused by the COVID-19 pandemic has motivated large federal, state, and local investments in academic recovery. However, the success of these efforts depends in part on students’ regular school attendance. Using newly collected data, I show that the rate of chronic absenteeism among U.S. public-school students grew substantially as students returned to in-person instruction. Specifically, between the 2018-19 and 2021-22 school years, the share of students chronically absent grew by 13.5 percentage points—a 91-percent increase that implies an additional 6.5 million students are now chronically absent. State-level increases in chronic absenteeism are positively associated with the prevalence of school closures during the 2020-21 school year. However, these increases do not appear to be associated with enrollment loss, COVID-19 case rates, school masking policies or declines in youth mental health. This evidence indicates that the barriers to learning implied by the sharp increase in chronic absenteeism merit further scrutiny and policy responses.