Students change classes in the halls at Walter Johnson High School on Wednesday in Bethesda, Md. (Ricky Carioti/The Washington Post)

In Montgomery County, a Washington suburb with sought-after public schools, Bethesda Elementary School opened an eight-classroom expansion three years ago to relieve pressure on the overcrowded campus.

A year later, the school spilled over again into a portable classroom. When this school year started Tuesday , it had four portables and 639 children — 80 more than it’s built to hold and 100 more than school system demographers predicted six years ago.

Bethesda Elementary is far from the most overcrowded campus in the Washington region. In Montgomery alone, half of the county’s 205 schools exceed 100 percent capacity, and some hover around 150 percent.

Montgomery’s approximately 161,500 students make it one of the largest school systems in the country, and it’s been growing by about 2,500 students every school year — the equivalent of a new high school.

But some parents say Bethesda Elementary is a good example of how enrollment forecasts — a key way that districts try to ensure enough capacity — can be significantly off, especially amid a building boom. In the area that Bethesda Elementary serves, more than 2,800 condos, apartments and other homes are under construction, have been approved or have been recently built, prompting fears that schools will be further swamped more quickly than anticipated.

“It’s frustrating,” said Stacy Kobrick, whose son attends Bethesda. “It feels like the county is putting economic development above the needs of students. We moved to this area to be in a good school, and they’re squished.”


Students change classes at Walter Johnson High School. (Ricky Carioti/The Washington Post)

School demographers across the Washington region cite a combination of factors that they say are difficult to predict, go beyond the boom in high-rise construction and signal vast lifestyle changes in urbanizing inner-ring suburbs. They say their crowded schools reflect the number of baby boomers beginning to downsize, more families unable to afford the costs of daily life, soaring home prices, an influx of immigrants and more families choosing to live in walkable, urban areas.

The growing shortage of affordable housing, they say, has thrown off predictions about the number of children coming from apartments and townhouses because more families are sharing housing to make ends meet. Other parents, particularly millennials, are increasingly raising children in smaller units to afford housing in suburbs and near walkable downtowns and transit. In Montgomery, townhouses recently surpassed single-family homes for the first time as producing the most schoolchildren per unit.

Montgomery Council Member Craig Rice (D-District 2) said the difficulty in forecasting enrollment shows how rapidly some suburbs are changing.

“We’ve built in assumptions for human behavior, and those dynamics are changing,” said Rice, who chairs the council’s education committee. “Is the priority a big house and a big yard anymore or being close and having the amenities? The paradigm for what families want is changing.”

While schools can add portable classrooms to deal with short-term enrollment fluctuations, parents say they too often become permanent. The crowding results in larger class sizes, jammed hallways, crowded playgrounds, congested parking lots, lunch periods starting midmorning, long cafeteria lines and increased competition for sports teams and school plays, parents say.

In the Washington suburbs, the problem has taken on new urgency as the economy has rebounded and sparked a flurry of apartment construction in areas closer to the city. Suburban planners have targeted some of the same areas, particularly near transit stations, for denser development as a way to accommodate population growth, limit traffic congestion and attract young professionals, along with the companies looking to hire them.

Officials say they are counting on such economic development to grow their tax bases to support an aging and increasingly poor population. New housing, some say, also will help keep home prices lower overall as supply catches up with growing demand.

But some parents say they worry their schools are being sacrificed for that economic growth, especially as school systems also try to keep up with high turnover in boomers’ homes and changing demographics.

West Potomac High School, in the Alexandria section of Fairfax County, is projected to be at 120 percent capacity this school year.

“Overcrowding is probably the number one issue for many parents,” said Matthew Dunne, whose daughter attends West Potomac. “We moved to Fairfax County for the schools, and we’re staying for the schools, but this is a problem that needs to be fixed and needs to be fixed soon.”

Washington-area school officials say some of the enrollment surge dates back to the Great Recession, when the region’s relatively stable job market attracted workers from other states and across the world. Public school systems also are still feeling the influx of children who switched from private schools during the economic downturn, officials say. Adding to the problem: As suburbs get built out, land for new schools has become increasingly scarce and expensive.

Alexandria City Public Schools opened Ferdinand T. Day Elementary School last week — its first new school in almost 20 years — in a converted office building. Last school year, nearly all of the city’s 17 schools exceeded capacity, officials said.

Younger families used to move farther out for larger and more affordable homes once their children hit school age, said city Planning Director Karl Moritz.

When the recession made getting a mortgage more difficult, many of them stayed, Moritz said. By the time the mortgage and housing markets loosened up, gas prices had spiked, leading some residents to forgo long — and increasingly expensive — commutes. Many also stayed to be in walking distance to parks, coffee shops and other amenities, Moritz said. Meanwhile, interest in taking care of a yard continued to wane as children spent more time away from home in organized activities.

“We’re not seeing people resume that old pattern,” Moritz said.

School officials say they’re also seeing more children from older apartments and townhouses, previously considered too small for families but now the only affordable option for many.

“Fifteen to 20 years ago, you might have a baby in a townhouse and then outgrow it and move to a single-family home,” said Jessica Gillis, facilities director for Fairfax County Public Schools. “More and more people are either choosing to stay in condos and townhouses, or they can’t afford to raise families in single-family homes.”

Many school systems say housing turnover in neighborhoods with empty-nesters is having the biggest impact.

Turnover is difficult to predict, planners say, because it’s highly localized and tends to hit neighborhoods in waves. A dozen or so homes selling over the summer can produce a dozen or more new students — the equivalent of half an elementary school classroom.

In Arlington, where schools have absorbed 44 percent more students over the past decade, officials say most new students still come from single-family homes, probably because of turnover. Moreover, as land values have climbed, some of the smaller 1950s-era houses on larger lots are being replaced with two or three homes on the same site, bringing more children.

Lisa Stengle, planning director for Arlington Public Schools, said more parents are forgoing larger homes to have shorter commutes and a more walkable lifestyle. Schools in south Arlington are “exploding,” she said, probably because it’s one of the few close suburbs where younger families can still buy a home for less than $600,000.

“Parents are very involved with their kids,” Stengle said. “If they have a two-hour commute each way, they can’t do that. Families are prioritizing that.”

Prince George’s County school officials say the affordable-housing crunch has sent more children their way, especially as families have been priced out of the District amid gentrification. Meanwhile, they say, they suspect many older apartments are producing more children because more families are living together to save on rent.

“We’re getting more students per [apartment] building,” said Shawn Matlock, director of capital programs for Prince George’s schools.

Rhianna McCarter, a Prince George’s schools planning specialist, said she suspects overcrowded schools in the northern part of the county are feeling the impact of international students who began arriving in greater numbers, many from Central America, in 2010.

“In some of our schools, we could get 300 new [international] kids in any one year,” said McCar­ter. “That’s pretty impossible to predict.”

School systems say they are making changes to improve their projections, particularly as some parents say planners are underestimating how quickly new high-rise apartments are being built and filling with children.

Essie McGuire, Montgomery schools’ executive director for operations, said its enrollment projections are about 99 percent accurate at a county level. But she said the countywide calculations have masked changes in individual neighborhoods. Statistically speaking, she said, it’s also more difficult to predict the future at a more detailed school level.

The school system recently hired a consulting group to help update its enrollment forecasting models and respond more quickly to rapid changes, particularly in high-growth areas.

“We just really felt the planning and demographic and land-use environment has changed so significantly in Montgomery County in recent years,” McGuire said. “We felt it was time to look at the tools we were using to see if adjustments needed to be made.”