Overall, the average student capacity in the system's eight western elementary schools is 77.6 percent. In the system's five other regions, average elementary student capacity ranges from 95.1 percent in the northern region to 111.8 percent in the northeastern region. Falling in the middle are the southeastern region, at 108.9 percent, and the Columbia East and Columbia West regions, at 105.4 percent and 101.5 percent, respectively.

The school system's three most overcrowded elementary schools are all in the east: Talbott Springs, in Columbia, at 131.2 percent; Waterloo, in Columbia, at 127.1 percent; and Veterans. The system's three most undercrowded schools are all in the west: West Friendship, at 75.0 percent; Triadelphia Ridge, in western Ellicott City, at 73.7 percent; and Dayton Oaks.

At the middle and high school levels, it is not necessarily the case that the west is undercrowded and the east overcrowded. But the trend is widespread enough at the elementary level to have garnered attention from county government.

"It's really a reverse of what was happening," said County Executive Ken Ulman. "We've got to make sure we stay on top of it."

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"We absolutely must make use of the school seats available, and that will help us keep the cost down to taxpayers overall," said County Council member Courtney Watson, an Ellicott City Democrat and former school board member.

She said a new school in the overcrowded Elkridge area, which she represents, is a must — Elkridge Elementary is at 108.7 percent of capacity — but utilizing open space in the west should be a priority.

"We have to be careful not to just build schools without first using up the extra capacity, and that's something the school board has to wrestle with," Watson said. "It's always a challenge to keep up with the shifting trends of where people want to live."

Economy cited as factor

Staying on top of the trend may be easier said than done, as there are a variety of factors at play, ranging from the broadly unpredictable, like the national economy, to the locally nuanced, like regional housing options.

Several officials pointed to the national economy in explaining the unbalanced capacity, saying the recession undercut projected growth on the system's western side.

"Some of those projections didn't come to fruition, and a lot of that, we believe, had to do with the economic slowdown," Roey said. "It's conjecture on our part, but we just weren't seeing families with the number of kids we thought showing up."

Kenny Smallwood, president of the Howard County Association of Realtors, said underprojected elementary numbers could also be a result of the local housing market. Parents moving their families to larger homes in the west are often "move-up buyers," he said, who are further along in their careers and whose children are beyond elementary school age.

The depressed economy has had the opposite effect in the east, producing student yields higher than expected.

Along the Route 1 corridor, more children than expected are coming out of multi-unit residential housing such as apartment complexes, as families downsize by moving in together or sending children to live with their grandparents, officials said. Certain neighborhoods in Columbia are suddenly producing more students than in years past as well, both for the above reasons and because older couples are selling their homes to younger families, including families moving to the area because of the federal Base Realignment and Closure (BRAC) process.

"The eastern portion of the county is where all the apartments and affordable housing is," Smallwood said, and that's what many families are looking for today, including BRAC families who have been unable to sell their homes elsewhere in the country.

"We just have a lot of change going on," said Marsha McLaughlin, director of the county's Department of Planning and Zoning.

"Whether that will be a little blip, and when the economy recovers we'll see people going back to regular patterns, we don't know," she said. "It makes it hard to plan when you're not sure if this is going to be a short-term or a long-term trend."

One size doesn't fit all

The county's mismatched capacity issues have also been driven in part by local school policies, officials said.

Before 2002, school capacity was projected for the entire system before being divided among regions and localities, a process that often created accurate overall projections but inaccurate individual school projections, said Gallihue, who has worked for the school system since 2006. The approach wrongly projected numbers in the west many times, he said.