Like many public school districts around the country, Centerville City Schools near Dayton started the year off remotely for the 8,000 kids it serves. Based on recommendations from local public health officials, the district didn't resume in-person classes until mid-October.

It didn't last. By late October, Superintendent Tom Henderson said the district was scrambling every day to find teachers for 90 to 115 classrooms, competing with other districts for substitutes. At one point, Henderson and his team were filling in teacher gaps hour by hour when substitutes and full-time teachers had planning periods. Crucial support staff members were also tough to find. Some days, they didn't have enough school bus drivers.

Too many people had either caught Covid-19 or had recently come into contact with someone who had it.

"Most of the exposure has come from outside of school," Henderson said. "The quarantines are just really hard to deal with."

The week before Thanksgiving, Henderson pulled the plug. Faced with rising case counts in the community and expecting positive case counts and associated quarantines to spike after the holiday, he shifted the district to remote learning until Jan. 19 — more than two weeks after New Year's Day.

Henderson said the local public health commissioner has acknowledged that schools are doing a good job preventing the spread of Covid-19 inside their buildings. But there's nothing they can do about the broader outbreak.

As the pandemic raged across the United States, experts warned that keeping schools open for in-person learning would become increasingly difficult if community spread went unchecked. Centerville's experience is an object lesson in that dynamic. Several other school districts announced similar shifts to remote learning over the holiday period.