Loudoun County Public Schools announced Thursday that it will return all students to online learning, a reversal that affects roughly 18,000 children who had gone back to school buildings over the past few months.

School officials in neighboring Fairfax County, meanwhile, shared a draft of a plan with a special school board meeting to return the system’s 186,000 students to in-person instruction in January. Officials also introduced an unusually lenient grading policy — meant to combat a spike in failing grades as the novel coronavirus pandemic continues to upend American education.

Loudoun’s decision, which takes effect Tuesday, will send home hundreds of high-schoolers, thousands of kindergartners through fifth-graders, very young children, students with disabilities and English-as-a-second-language students.

Some of that cohort benefited from almost a full semester of face-to-face instruction — the earliest returnees, 900 high-schoolers at the Monroe Advanced Technical Academy, stepped back to their buildings on Sept. 8. Others returned over the course of October. But roughly 7,300 students have been back in classrooms for only about a week, having resumed in-person schooling Dec. 1.

In a message to families announcing the switch, Loudoun Schools Superintendent Eric Williams wrote that he recognizes the abrupt backtracking will cause chaos.

“We understand that this process is disruptive for families of students who have been participating in hybrid in-person learning this fall,” Williams wrote. “The safety and well-being of all students, staff members, their families and the community continues to be our highest priority, and this decision is being made consistent with our commitment to achieving that objective.”

In Fairfax County, so far slightly more than 5,000 children have reentered classrooms; under the tentative timeline discussed Thursday, the rest of the student body would begin heading back on Jan. 12, with all who choose face-to-face learning fully returned by Feb. 2.

On Thursday, school officials also disclosed a new grading policy that is to take effect in early January. The policy directs that students cannot receive grades lower than 50 percent, minimizes the penalty allowed for late work, says any one assignment can count for at maximum 20 percent of a student’s final grade and reduces the minimum number of assignments per class per quarter from nine to six.

Fairfax is further examining how it can offer greater “flexibility” regarding end-of-year examinations and grades, Chief Academic Officer Sloan Presidio said at the meeting, and the district plans to enhance its summer-school offerings to help students catch up.

These grading changes have come as a direct response to a worrying report, released by Fairfax last month, that found failing grades had risen dramatically in the era of online learning: The percentage of middle school and high school students earning F’s in at least two classes jumped by 83 percent, from 6 percent of those students to 11 percent. That meant close to 10,000 children earned at least two F’s, an increase of more than 4,300 students from this time last year.

Presidio called the percentage of F grades highly concerning, adding that anecdotal evidence also suggests children are struggling.

“We continue to hear from our students [who] have concerns about the impacts of grades on their future . . . who feel disconnected from peers and teachers,” Presidio said. “They feel overall that as a school system, we’re not doing enough to hear them, listen to them and address their needs.”

And the district’s most vulnerable students struggled most — the percentage of students with disabilities receiving at least two F’s   jumped   from   9   percent   to 19 percent, and the percentage of English-learner students in this category jumped from 17 percent to 35 percent.

On Thursday, Fairfax officials announced they planned to target these populations specifically. In coming weeks, staffers will conduct family conferences with the parents of every child in either group who is earning D’s and/or F’s. For the families of English-learner children, these conferences will be conducted in that household’s native or primary language.

Fairfax also will work to ensure English-learner students have access to the Internet and will require that all teachers complete an hour-long training — “Essential Practices for English Learners” — by Feb. 1.

In addition, case managers for children with disabilities will check in with students every two weeks. For children in this group who are earning D’s and F’s, case managers will work to develop “plans of support,” according to a presentation prepared for the meeting.

The twin developments in Loudoun and Fairfax come as coronavirus cases and deaths continue to spike dramatically nationwide and in the Washington region. On Thursday, coronavirus deaths in D.C., Maryland and Virginia passed 10,000, and the seven-day average of new daily infections rose to a record 6,989.

The new wave of cases spurred Virginia Gov. Ralph Northam (D) to issue an expanded mask mandate, place stricter limits on social gatherings and impose a curfew asking people to stay home late at night.

Also Thursday, the head of the Virginia Education Association — one of the state’s most powerful teachers associations, with 40,000 members — called on Northam to order all public schools to go virtual-only until at least mid-January.

“We know that virtual learning is not a true substitute for the in-person instruction we have embraced for generations, [but] it IS the safest and wisest course,” the association’s president, James F. Fedderman, said in a statement. “Learning losses will be made up, but loss of life cannot be.”

Williams, in his note to parents, wrote that two particular statistics for Loudoun County had caused the school system to close its classrooms again: The total number of new cases per 100,000 people in the county had stayed above 200 for more than five consecutive business days, and the county’s positivity rate for coronavirus tests had remained above 10 percent for the same time period.

The school board had previously voted that if both of thresholds were met, the Loudoun district — which enrolls roughly 82,000 students — would have to close its classrooms to students completely.

Williams revealed little in his message about when classrooms might be able to reopen. At a school board meeting next week, he wrote, “LCPS will further discuss plans for using these metrics to determine when hybrid in-person learning could resume.”

So far, it does not appear that Loudoun’s reopened school buildings functioned as superspreader sites. The school system has reported 166 positive cases of the virus among staff members, and 94 positive cases among students, since Sept. 8.

At present, 112 staff members and 24 students are in quarantine, according to school system’s website.

But it is thought to be unlikely that these cases developed or spread inside school buildings. Loudoun is pursuing a policy of publicly reporting all cases among its staff and student body, whether the infected individual is working or studying on a campus.

And, as of last Friday, the Virginia Department of Health reported that Loudoun County was witnessing no coronavirus outbreaks inside schools. The department defines a school-associated outbreak as at least two confirmed cases of the virus, and in which “transmission [took place] within the school facility or at a school-sponsored event among students, faculty, staff or visitors.”

For the past several weeks, Loudoun had been by far the most aggressive of Northern Virginia school districts in its push to return students to classrooms, continuing to welcome children even as peer school systems were backing away from face-to-face learning.

Alexandria City Public Schools recently opted for online-only learning for all of its 16,000 students, after returning just six children to school buildings. Arlington Public Schools, which enrolls 23,000, chose to postpone returning lower-schoolers to classrooms until 2021.

And last month, Fairfax Schools Superintendent Scott Brabrand announced that he was halting his plans to return thousands of students to buildings in November and December. He also sent more than 3,000 students back to online-only instruction, leaving roughly 5,500 children still participating in a couple days each week of in-person learning. That group is composed of high-schoolers in career preparatory programs, young children with autism, some students with disabilities and some English learners.