Enrollment in Snohomish County classrooms rose modestly this fall, with more than 500 extra students bringing in the equivalent of about $2.7 million in state funds.

But the extra change does not reach all pockets.

The ruling trend continues to be new housing developments, concentrated primarily in the north and east of Everett, including Marysville, Lake Stevens, Snohomish and Monroe.

Hot spots also include Mukilteo, which saw the area’s largest gain. Meanwhile, districts including Edmonds, Sultan and others lost students.

Projecting enrollment accurately is key for districts since more than 70 percent of their budgets is based on the number of students in their classrooms. Districts receive about $5,200 from the state per full-time student.

Housing, birth rates, population trends and job losses all figure into projections. But there are usually some surprises, too.

Mukilteo has been experiencing an enrollment windfall of sorts, particularly at the high-school level. In October 2003, Mukilteo had 958 juniors enrolled in its schools. One year later, that same class included 1,032 seniors.

“It’s a mystery,” said Andy Muntz, a school district spokesman. “We don’t know where these kids came from.”

A consultant who follows enrollment trends is trying to figure it out.

Growth can bring growing pains. Right now, $163.4 million worth of building is under way in the Monroe and Snohomish school districts to relieve crowding.

Lake Stevens and Marysville hope to join the building boom. Each likely will bring proposals for new school buildings to local voters early next year, totaling up to $130 million.

For now, Lake Stevens is compensating with 61 portable classrooms, most at the middle and high schools.

“It’s (the equivalent of) three elementary schools in portables,” business manager Terry Heindl said. “So we know we have to do some building and changing.”

Enrollment in Marysville increased nearly 2 percent compared with last fall, when dozens of families enrolled children elsewhere during a state-record 49-day teachers strike.

In the past five years, Marysville’s enrollment has taken a roller coaster ride but the net effect has been relatively flat.

Now, district officials are expecting significant growth the next five years. There are roughly 3,000 housing lots in various stages of development.Meanwhile, Darrington School District continues to feel the pinch of declining enrollment, which has dropped almost 9 percent in five years.

“There is a lot of mobility,” Superintendent Randy Swenson said.

One good sign, Swenson said, is kindergarten enrollment increased this fall, and they tend to stay in the district, he said.

Still other districts are simply seeing more of the same.

Growth in Mill Creek has helped Everett stem its losses. The district lost 132 students, about 1 percent less than last year.

Similar losses are expected the next few years, said Mike Gunn, director of facilities and planning.

“If we get a good housing industry here in the area … that will help pull us up,” he said. “But basically we see more of the same – heavily dependent on Boeing and housing.”

Reporter Melissa Slager: 425-339-3465 or mslager@heraldnet.com.