Tens of thousands of children in the Washington suburbs are returning to in-person schooling this week, marking the end — for many — of more than a year of wholly virtual instruction.

Montgomery County, Maryland’s largest school district, opened the doors of its 135 elementary schools to more than 19,000 children from kindergarten to third grade. For the kindergartners, the day meant taking their first steps ever inside their schools.

“It’s the day we’ve been waiting for,” said Cynthia Simonson, president of the Montgomery County Council of PTAs.

Over the next few days, three major districts in Northern Virginia will send large cohorts of middle-schoolers and high-schoolers back into classrooms, where they will join peers who returned earlier this semester. This final phasing-in fulfills promises, issued separately by leaders of the systems in Fairfax County, Arlington and Alexandria City, that families who prefer it will be able to pursue in-person learning by mid-March.

In Montgomery County, Monday also heralded the return of some students enrolled in ­special-education and career programs, as well as seniors whose grades have put them in danger of not graduating. This week’s returnees joined more than 700 students who had returned March 1, a group made up mostly of special-education and career program students.

Of course, back-to-school day looked a little different from previous years — and not just because it was taking place in mid-March.

On Monday, officials asked Montgomery families to complete a health form attesting that their children did not have coronavirus symptoms or recent exposure to people who tested positive for it.

Once inside the building, everyone wore masks, and children were confined to desks set six feet apart. Some in-person students learned from teachers who had opted to stay home and were present only virtually, as faces inside devices set up on children’s desks.

And sometimes, even when the teacher was lecturing at the front of the room, students kept watching them through a Chromebook screen. This tactic is meant to facilitate an instruction model known as “concurrent” teaching, in which educators must simultaneously lead lessons for in-person children and those learning remotely from home.

That was the setup in Sophia Hoppe’s third-grade classroom, she said. She was looking forward to finally meeting her teacher at William Tyler Page Elementary School in person, but for much of the day she sat with headphones in, dividing her attention between the teacher on her Chromebook screen and the same teacher standing before her in the classroom.

The morning was a little frustrating, she said, because a delay in the Zoom video created an echo: a niggling gap between what Sophia was hearing in the classroom and what was being piped into her ears. That issue was resolved by the afternoon, Sophia said.

Still, she had to remind herself to look up at the real person standing right there and teaching her.

“Sometimes I’d take a glance,” Sophia said. “I am usually more focused on the screen, though, because there were some kids talking during class.”

Her mom, Beatrice, predicted Sophia, 9, would soon remember how to learn inside a classroom again. “You’ve just gotten used to being on Zoom,” she said. “For six months or however long we’ve been at it.”

But overall, Sophia said, she loved every minute of her first day back, no matter the Zoom glitches. The first thing she — and her brother Theo, a first-grader — shouted when clambering into the car after school was, “It was amazing!”

Later, Theo, 7, explained why: “It was amazing because I got to see my friends, talk with them and play with them.” The only thing he didn’t like was lunch: The turkey sandwich was okay, but he hated the side offerings of raisins, hummus and chocolate milk.

Their mother, who belongs to the pro-reopening parents organization Together Again MCPS, said she feels fortunate because her children were among the earliest large groups to return. Still, Beatrice Hoppe said she is disappointed in the school system for taking so long to reopen — and for stretching its return of students over six weeks or more.

Other families will not see their children in school again until late April, she said.

“It’s been such a slow process,” she said.

Together Again MCPS launched a petition over the weekend demanding that students return to school more quickly. The group wrote that other school systems are phasing students into classrooms over a period of one to three weeks.

By comparison, Montgomery is “moving at a snail’s pace with inappropriately long phasing-in plans that keep children, particularly teenagers who are most at risk for depression and self-harm, home for upwards of six more weeks,” the petition reads. “Nearly 50% of MCPS high schoolers will not return until the final week in April.”

D.C. public schools reopened its buildings districtwide on Feb. ­­2 for around 20 percent of its students, and Northern Virginia systems started returning children to classrooms shortly after that, although they have proceeded more slowly than officials in the nation’s capital. Fairfax County Public Schools, Loudoun County Public Schools, Arlington Public Schools and Alexandria City Public Schools all stretched their returns over a month or less.

This week, Fairfax — with 186,000 students, the largest district in Virginia — will return about 27,500 third- through sixth-graders and special-education students. That will bring its in-person total to more than 84,000 students, representing about 47 percent of the student body. The rest will continue to learn virtually.

Loudoun has returned slightly fewer than 30,000 students, according to spokesman Wayde Byard, or about 36 percent of its student body.

Arlington is slated to return thousands of seventh-graders, eighth-graders and 10th- through 12th-graders Tuesday and Thursday. That school system’s cumulative count of in-person learners will come to about 17,000, said spokesman Frank Bellavia, or 64 percent of enrollees.

And in Alexandria, slightly more than 3,700 children will reenter classrooms this week, joining about 1,600 of their peers who have already headed back to campus. Alexandria expects to return close to 5,400 students in total, said spokeswoman Julia Burgos, equivalent to 34 percent of the student body.

In Bethesda, Loren Murad worried as she watched her first-grader, Irene, bounce off to school at Bannockburn Elementary on Monday morning. Would the safety precautions prove sufficient? Would her daughter miss the routine of home?

“But then she had just a big, big smile on her face when she came out this afternoon,” Murad said. “And hearing her rattle off her full day, unprompted — which is not her usual style — we knew she really did enjoy it.”

Murad’s older child, 9-year-old Caroline, peppered her sister with questions: “Where was your desk? How did you know it was time for lunch?” Caroline, a fourth-grader, was feeling left out because she will not start in-person learning for some weeks.

And one thing Murad will not forget: the way her two children got caught on certain, once-obvious details of the school day.

“They were marveling that the teacher can see them now directly [during a presentation], when they’re raising their hands,” Murad said.

In the era of Zoom, they had forgotten how that worked.