As cases of the coronavirus surge nationally and in the D.C. region, some Washington-area school systems are pressing pause on plans to return children to classrooms.

Arlington Public Schools in Northern Virginia, which enrolls 26,000, this week delayed returning lower-schoolers to buildings until 2021. Anne Arundel County Public Schools in Maryland, which serves roughly 85,000, followed suit Wednesday, pushing back a scheduled return for elementary students until February. D.C. Public Schools also nixed its plan to bring some students into classrooms Nov. 9.

“We continue to see the case incidence rate in our area increasing, not decreasing,” Arlington Superintendent Francisco Durán wrote in a message to families Monday. “Moving too quickly . . . while case levels are rising, represents a safety risk and could cause further disruption to schedules.”

Most large public school systems in D.C., Maryland and Northern Virginia have been shuttered since March. But as fall got underway, superintendents in all three began announcing strategies to deliver small batches of vulnerable students — those with disabilities, English-language learners and young children — back into classrooms.

As coronavirus cases held steady for much of August and September, small groups of children settled successfully into some classrooms in Northern Virginia. And school officials got more ambitious, debuting strategies for returning larger cohorts of kids — stretching into the thousands — to campuses.

But the D.C. area’s plateau in cases ended as the weather turned colder. In October, cases began to pick up, with the daily count exceeding 2,000 for the first time this fall. Late last month, D.C. hit an 11-week high in new daily infections, and officials in Maryland’s Montgomery County reported the highest number of cases seen since June.

Teachers unions in the Washington region, noting the spike, began mounting vocal challenges to officials’ reopening plans. In Virginia’s Fairfax County and in D.C., teachers held mental health days — during which they did not teach — to protest reopening plans. When D.C. this week nixed reopening plans, which would have brought 7,000 elementary students for in-person instruction next week, officials pointed to teachers’ reluctance to return.

“Our plans were blocked,” D.C. Public Schools Chancellor Lewis D. Ferebee said. “We did not have the ability to utilize our staffing model.”

Arlington officials had hoped to return thousands of prekindergarteners through fifth-graders — including English-language learners, children with disabilities and career and technical education students — to classrooms for two days of face-to-face instruction each week starting Nov. 12. Now, no one in that group will see the inside of a school building until at least January.

According to a presentation from Durán, children in this cohort will instead participate in a phased return over the course of January. Prekindergarten, kindergarten and career and technical students will return first, then first- and second-graders and finally the last batch, which will include third-, fourth- and fifth-graders. Middle- and high school students who chose hybrid instruction are to return sometime in January, yet to be determined.

Still, Arlington did proceed with a portion of its previous reopening plans this week. Officials returned 236 students — some with disabilities — to classrooms Nov. 4, as part of what the school is calling its “Level 1” cohort. The group whose instruction was delayed is known as “Level 2.”

In Anne Arundel, elementary students were supposed to begin learning inside classrooms starting Nov. 16. But the county school board voted Wednesday in favor of pushing that return back to February at the earliest, after Superintendent George Arlotto gave a speech asserting the county’s case levels had risen too high to permit a safe reopening.

“The case rates numbers in Anne Arundel County are going in the wrong direction,” he said, because the seven-day average of infections had risen above 15 per 100,000 residents.

The delays, although acclaimed by some as wise, drew ire from parents frustrated with the limitations of online learning. A recently formed advocacy group in Northern Virginia, Arlington Parents for Education, released a caustic statement slamming the superintendent’s new, slower reopening plan, arguing it will harm children.

“We have to learn to live in a world where Covid exists AND children are allowed to attend school,” the group wrote in a statement. “Arlington’s children will feel the effects of this decision for years to come.”