Student enrollment has dropped markedly this year in school systems across the Washington region, with thousands of children exiting public schools amid the pandemic and officials projecting millions of dollars in potential budget fallout.

The decline comes as some families have switched to private schools with in-person learning, rather than sticking with the all-virtual approach of their public schools. Others have decided to take on home schooling or move to farther-away school districts.

The region’s largest school systems stand out for their sheer numbers: Virginia’s Fairfax County lost more than 8,700 students since last year. Maryland’s Montgomery County is down 3,700 students, according to preliminary figures. In D.C., leaders say they expect a drop of somewhat less than 5,000 traditional public and charter students.

The school systems are among many others in the area posting enrollment losses of 2 to 5 percent — and part of a broader enrollment downturn nationally. It is driven partly by families with children in prekindergarten and kindergarten, some of them giving up on remote learning for children so young.

The cost is only beginning to become clear: potentially $42 million in Montgomery County and $35 million in Prince George’s County, with major pots of funding tied to student counts, according to officials in the two school systems.

“For local governments and school districts, this will be a very tough year,” said Michael Herbstman, chief financial officer for Prince George’s County Public Schools.

Enrollment in Prince George’s County is about 132,000 this month, down 3,939 students — one part of a difficult budget picture. Monica Goldson, the district’s chief executive, announced cost-saving measures in mid-October, including a freeze on most overtime and all but some school-based jobs, with a reduction in school-based funds by 10 percent.

Since the pandemic hit the region in March, public schools in the Washington area have been scrambling to adjust to unprecedented challenges in education. All of the region’s school systems started this fall with distance learning.

Only recently have some begun to bring children onto campus.

Renee Zapadka, a mother of two in Potomac, said she and her husband had planned to send their son to their neighborhood elementary school but changed their minds, deciding to keep him at a private preschool that offered in-person kindergarten.

The risks are minimal and the boy wears a mask without complaint, Zapadka said.

“He came home one day and said, ‘Mom, do you know about photosynthesis?’ ” she said, recalling her surprise that the concept came up at his age. “I’m confident that he is learning, and I don’t think he would have learned as much.”

Now, the family is considering moving their sixth-grade daughter, who is struggling through her first year of middle school remotely.

In Montgomery County, the pandemic brought years of growth to a halt. For more than a decade, its numbers had surged, up more than 15,000 students since 2011.

Last year, it recorded more than 165,000 students — and projected a jump of 2,500 this fall, similar to its increase last year. But it did not go as planned. It’s at 161,148 for prekindergarten to 12th grade.

The pandemic touched off a reassessment for many families.

Recent data about withdrawals show that 1,080 students left the Montgomery system for home schooling — compared to 74 for the same period the previous year. Almost 1,020 left for private school outside of Montgomery, compared to 148 the previous year. Students moved to private schools within the county, too: 200 more than in the previous year.

In Silver Spring, Deborah Schoenfeld was one of them, switching her 6- and 8-year-olds to the St. Bernadette Catholic school, which offers in-person instruction five days a week.

She and her husband graduated from county schools and have family members who work for the school system. But the system appeared to lack urgency and a strong vision, she said, and she did not want more online learning for children so young.

“I know that it’s better this year, but I don’t think it’s a true substitute for in-person learning,” she said.

In Virginia, enrollment slipped as much or more. Fairfax, with 189,000 students last year, shrank by 8,736 students, about 4.6 percent. Loudoun’s student body of nearly 84,000 dwindled by 2,429, about 3 percent. And Arlington’s 28,000-student enrollment fell by 1,256, about 4.5 percent.

How the decline will affect the bottom line is still being sorted out.

Loudoun will see a reduction in state revenue of about $15.3 million this year as a result of lower enrollment for 2020-2021, said schools spokesman Rob Doolittle.

Roughly a third of Loudoun students who withdrew — just over 1,400 — transferred to private school. Another 1,130 chose home schooling, with nearly 900 picking a public school in another state and almost 700 choosing another public school in Virginia.

Arlington spokesman Frank Bellavia said the system is waiting to hear how bad the damage will be. “We are expecting a drop in state revenue since that is tied to enrollment,” he said.

Fairfax and other systems said they are asking the state to hold off on any funding changes for districts with enrollment declines — at least until schools are able to get more kids back in classrooms, spokeswoman Lucy Caldwell said.

“We do not know how many students will return to school when buildings reopen but would anticipate that the numbers will rise,” Caldwell said. “This will be a challenge to balance if the budget is reduced prematurely.”

The possibility of big cuts in funding has many in Maryland deeply concerned.

“There is a decrease in enrollment to our public school systems, across every district, of roughly 3 to 5 percent,” Patricia Saelens, president-elect of the Public School Superintendents’ Association of Maryland, told the state board of education this week.

That could mean funding losses from $1.7 million to $60 million in each school system, she said, asking the board to advocate to Gov. Larry Hogan (R) “to hold us harmless for next year’s budget.”

In Howard County, enrollment fell by about 1,600 students, to 55,810, according to preliminary figures that must still be finalized by the state. The drop could contribute to a potential $17 million loss in funding, though officials said other factors play a role.

Under Maryland’s system, enrollment on Sept. 30, 2020, would help determine certain types of funding for the fall of 2021. Low numbers mean less money, even though many expect an enrollment rebound by next fall.

“We fully expect a return to essentially regular enrollment next year,” said John Woolums, government relations director of the Maryland Association of Boards of Education.

Maryland school boards are asking lawmakers to address the mismatch by passing a bill that would use September 2019 enrollment numbers for funding calculations, or use an average of three years, Woolums said.

“Students in all 24 school systems will certainly benefit from state and county education budgets that maintain as high a degree of stability and predictability as possible in these extraordinarily turbulent times,” he said.

In the District, city leaders issued a plea to the public at the beginning of the year, alarmed that 20,000 students who were expected to enroll had not yet.

Unlike most districts, D.C. students are required to re-enroll each year, even at the same school. But the pandemic made the process more difficult. No longer could parents just stop by the schools’ front desks during drop-off and pick-up times.

By late September, the picture was less grim, with officials estimating a decline of less than 5 percent. Last year, the city served 99,000 traditional and charter school students, a figure that includes adult learners, most of whom have not received high school diplomas. This adult learning population has experienced a substantial decline in enrollment.

The other big enrollment drop came in prekindergarten and kindergarten grades, which lost more than 2,300 students, according to the latest public data in late September. D.C. officials said they expect stronger enrollment numbers after their final count.

Children are not legally required to attend prekindergarten grades, and many families have opted instead for day cares that provide in-person care and accept vouchers from qualifying families.