Public-school attendance across the U.S. has dropped to unusually low levels, complicating efforts to keep schools open, as districts also contend with major staff shortages.

Many students in kindergarten through 12th grade are out sick because of Covid-19 or are being kept home by anxious parents, as the Omicron variant surges, officials say. Remote learning often isn’t being offered anymore for students who are home. Empty desks create a quandary for teachers, who must decide whether to push ahead with lesson plans knowing a large number of their students will need to catch up.