As students in Northern Virginia settle back into classrooms — and face the disruption of coronavirus quarantines — school officials are swiftly adjusting the rules of bricks-and-mortar instruction to keep pace with the ongoing pandemic.

Administrators are fleshing out quarantine instruction plans, adding virus testing and vaccine mandates for students and staffers alike, and are considering how to deliver shots to families, including to young children, should federal health agencies approve a vaccine for those under 12. This planning is underway as Virginia hits a major educational landmark: All 132 school divisions are offering full-time, in-person learning, Gov. Ralph Northam (D) announced this week.

“I am proud,” Northam said in a statement Thursday, that “Virginia’s children are now safely back in school.”

But what school looks like, and what it entails, keeps changing. This week, officials with Fairfax County Public Schools — whose approximately 180,000 students make it the largest district in Virginia — announced that students in quarantine will receive live-streamed instruction, where before they worked mostly on take-home assignments. On Thursday, Fairfax’s school board also proposed that Schools Superintendent Scott Brabrand start planning for mass distribution of “children’s vaccines.”

In neighboring Loudoun County Public Schools, which enrolls about 81,000, administrators said they are shrinking the required quarantine time for students exposed to the coronavirus from 14 days to 10.

And in Alexandria City Public Schools, a district of 16,000 across the Potomac River from the nation’s capital, the board voted unanimously Thursday to require that students participating in winter or spring sports this academic year provide proof of vaccination to train or compete. Alexandria follows Loudoun, Fairfax and Arlington Public Schools, which already adopted such mandates.

The board also voted unanimously to require that Alexandria staffers submit documentation proving they are fully vaccinated by Nov. 15. Staffers who fail to do so may be put on leave without pay or be fired. Exemptions will be offered only to employees who “satisfactorily” demonstrate they cannot receive the vaccine for medical or religious reasons, and these staffers will be tested weekly.

As of Thursday, 2,225 Alexandria staffers are fully vaccinated, while 362 are not vaccinated and are undergoing weekly testing, officials said. Of these, 15 are administrators, 138 are licensed as teachers and 209 are support staffers such as bus drivers, meal deliverers and cleaners.

The rule may be tough to swallow for some. During public comment Thursday, one woman who said she was speaking on behalf of some school employees — but whom an Alexandria spokeswoman said does not work for the district — urged the board not to require vaccinations for staffers, complaining in part that developers of the Pfizer-BioNTech and Moderna vaccines used cell lines from aborted fetal tissue to test whether the shots worked.

Early in the evening, board member Christopher A. Suarez, who has emerged as a strong advocate for mandatory vaccination, asked the superintendent whether Alexandria would eventually consider issuing a vaccine requirement for all students older than 12, and not just for athletes.

Alexandria Schools Superintendent Gregory Hutchings Jr. and his staff said it is important to target student-athletes in particular because national data from the past year and a half shows that sports teams and events often contribute to coronavirus outbreaks. Besides, students already are vaccinated at high levels in Alexandria City, said Julie Crawford, chief of student services and equity.

Suarez was not convinced. “I do think we need to continue to have the conversation about all students,” he said.

Crawford said the school system soon will have its own data on student vaccination rates. School officials are sending a survey to families of students 12 and older to ask whether their children have been vaccinated and, if not, to see whether their children would be interested in receiving the shot at school, Crawford said. Alexandria is developing a plan to transport students 12 and older to receive vaccinations, probably starting in early October, she said.

In Loudoun County, Superintendent Scott A. Ziegler announced last week that he was shortening the quarantine period for unvaccinated or partly vaccinated students exposed to the virus from two weeks to 10 days. Ziegler attributed the decision in part to the “extremely low number of student cases” Loudoun has seen since reopening for in-person learning for the vast majority of students on Aug. 26.

As of Sept. 17, Loudoun had seen 69 cases of the virus among students and had sent 259 into quarantine for possible exposure.

“For a lot of children and their families, quarantining for 14 days is a hardship, economically and in regard to their mental health,” Ziegler said in a statement.

Speaking at a board meeting Tuesday, he added that Loudoun eventually could shift to requiring only seven days of quarantine, provided that the student concerned tests negative for the virus after the fifth day.

In Fairfax, officials on Tuesday debuted a program of virtual video instruction for children who must isolate because they contracted the coronavirus or were exposed to the virus. The initiative, which Fairfax is calling “StreamIn/CheckIn,” will permit students to watch their classes online, although teachers can choose whether to stream live or record and post the video later.

Remote students will be able to watch and listen, but their camera and audio will stay off, Fairfax officials said. This setup is meant to avoid forcing teachers to pursue the concurrent instruction model, which requires educators to engage with online and in-person learners simultaneously and which many teachers found severely taxing at the height of the pandemic.

Still, some teachers fear the plan will greatly increase an already large workload. The Fairfax Education Association, which represents roughly 4,000 employees, is calling on the school system to give educators required to teach quarantining students some form of compensation.

The union “is asking FCPS to provide additional time during the school day or additional compensation for hours spent beyond the contract day, in order to make their quarantine student support plan a reality,” association president Kimberly Adams said Friday. Fairfax schools spokeswoman Helen Lloyd said officials plan to review the request next week

During quarantine, students in isolation will be able to access their class assignments via the learning platform Schoology, and they will attend check-ins every other day with teachers to receive academic and social-emotional support. Quarantine education will look different for different grade levels: Elementary-school students will be able to watch videos only of their language arts and math classes, while middle- and high-schoolers will be able to stream every class except for physical education.

The StreamIn/CheckIn program will begin Sept. 27, officials said. It will kick in for every isolating student by no later than the third day of the student’s quarantine.

Also Thursday, Fairfax School Board member Melanie K. Meren suggested that the superintendent convene a group of “community stakeholders” to start figuring out how to deliver vaccines to children in the county. The board will vote on her suggestion at its next meeting.

The proposal comes shortly after the drug companies Pfizer and BioNTech announced that a lower dose of their vaccines was safe for children as young as 5 and triggered a robust immune response in this population. Although the companies still have to submit their data to the Food and Drug Administration, which they say they hops to do by the end of the month, the finding is a key step toward the vaccination of younger school-age children.