In a surprise move, Arlington Public Schools is scrapping a plan to offer in-person and virtual learning this fall and will instead require its 28,000 students to start the school year 100 percent online.

The district’s superintendent, Francisco Durán, announced the switch in an email to families Tuesday afternoon, citing a recent increase in coronavirus cases nationwide. He also wrote that he is proposing that the school system push back the start of the school year by about a week to give teachers and administrators more time to prepare.

Durán will formally present both suggestions to the school board this week. The board will vote on the delayed start, but the decision to go all-virtual is not subject to board approval, according to school spokesman Frank Bellavia.

“Throughout our planning, the health and safety of our staff and students has been our top priority, and beginning the year with a virtual model allows us to continue to monitor the situation until we are confident it is safe to return,” Durán wrote in the email, adding, “I want to emphasize that this decision weighs heavily on all of us.”

Also Tuesday, Manassas City Public Schools announced that it will begin the school year virtually, and the school board also approved moving the first day for students to Aug. 31. The district said its goal was to offer in-person learning again “when it is deemed safe to do so.”

“The School Board did not take this decision lightly,” Superintendent Kevin Newman said in a message on the district’s website. “Although there is a strong desire to have everyone back on campus, the health and well-being of students and staff remain the Board’s top priorities.”

The decision by the Northern Virginia districts comes as President Trump and members of his administration pressure school districts throughout the country to reopen school campuses as normal, for five full days a week, in the fall. It also bucks a trend: Most other school systems in the region are allowing families to choose between a fully virtual learning option and a hybrid education plan that combines a few days of in-person instruction with online teaching each week.

Nearby Fairfax County Public Schools, among the school systems offering a mixed option, has twice drawn heavy criticism from Education Secretary Betsy DeVos over the past week. She has insisted that by refusing to reopen full time, the district is failing its students.

Under Arlington’s new guidelines, teachers and staffers would return to school in late August so they could undergo professional training on teaching virtually. Students would begin online lessons Sept. 8. Depending on rates of coronavirus infection and the death toll in the county, the superintendent wrote, the school system may transition some students to in-person instruction as early as October.

The school system’s original plan, unveiled in late June, allowed Arlington parents to pick between 100 percent distance learning and a model in which students would attend school two days a week in person, while spending two days each week learning at home, taught virtually by a teacher.

One day a week — Mondays — would have been set aside for “self-directed instruction.”

That plan drew backlash almost immediately, from parents and teachers on both sides of the issue. Those who opposed any face-to-face instruction mounted an especially swift and coherent campaign.

The Arlington Education Association, which represents teachers, wrote a public letter to the superintendent and the school board warning that sending students and teachers back to campus would lead to “illnesses and death.” And more than 2,300 people signed a petition calling on Arlington to switch to a 100 percent virtual model of learning for the fall.

The extremely detailed reopening plan outlined in that petition, which runs to almost 1,000 words, closely resembles the online-only program the superintendent announced Tuesday.

Laura Yellin, an Arlington teacher who works with deaf and hard-of-hearing students, was among those happy to learn of the reversal. Her job requires that she travel between three to five schools every day, working one-on-one with students at each campus, so she would have been at extra risk if schools reopened.

She thinks online teaching will be safer for everyone, given the surge in coronavirus cases nationally. And virtual lessons may actually be better for some deaf students, she said — because, back in classrooms, teachers would have to wear masks.

“If people don’t have clear masks on it’s a real challenge to read lips” or read facial expressions, said Yellin, who also is deaf. “It’s tough ... with masks, I don’t always understand when people are talking to me.”

Durán wrote in his email that he recognizes many Arlington families had begun planning for the earlier model and may be feeling confused or be thrown into chaos by the sudden change.

“We recognize that this change will present challenges to many of our families,” he wrote, “and I hope that by informing you now, you will be able to make necessary adjustments to your plans for the fall.”

For Arlington parent Laura Porter, the change solved a family argument. Her husband had advocated virtual instruction, while she’d been pushing the hybrid option, eager to provide her daughter, an eighth-grader, with some social interaction.

But she gave it up without regret on Tuesday.

“I think starting the year this way makes sense, because there are just so many unknowns,” Porter said.

Her daughter is okay with it too, she said: Although her daughter will miss her friends, at least now everyone will be stuck at home. The eighth-grader had worried she’d be the only one of her group of friends to select all-virtual learning.

Porter and her husband have both worked from home successfully for months, she said, so child care won’t be an issue for the family.

“But I do feel for parents who have to go in to work, especially if they have young children,” Porter said. “I hope the school finds a way to support them.”