Appeal Elementary School had five lunch periods, eight portable classrooms and three sessions of assembly last year to accommodate its 726 students, 206 more than it was built to hold. It was the most crowded school in the state's fastest growing county.

This year, Calvert County opened a new elementary school to ease crowding at Appeal and other schools in the rapidly swelling southern end of the county. Relief was supposed to be felt by all.

But it didn't work out quite the way officials planned. On the day it opened, Dowell Elementary was over capacity, with some classrooms holding as many as 30 students, far more than Principal Kathryn Alvestad had hoped for. Now school officials are coming to terms with the fact that even the best plans can be thrown off course by the housing boom in the outer Maryland and Virginia counties that surround Washington. And outlying districts are not alone as shifts in population and demographics have crowded new schools in Montgomery and Prince George's as well.

"People come and build and you can't predict how many children they'll have," said Ruth T. Keimig, a Calvert school board member.

The Dowell situation is a symptom of the pace at which school populations are growing in places such as Calvert. Families drawn to communities on the outer edges of the Washington area by affordable housing and new employment centers are filling local schools to the bursting point. School officials have responded with frequent redistricting and by building and expanding schools.

Staff members spend years planning and designing schools and making educated guesses about how many students they will need to accommodate. "You're using data to predict what will happen and you don't always predict right," said Jim Marlett, director of school facilities in Calvert.

The numbers also have proven fickle in some of the Washington area's largest school districts, where brand-new schools and replacement schools are filling up shortly after opening, much to the dismay of parents who had visions of small class sizes and plenty of extra space.

Adela Acosta, principal of Parkway Elementary in Prince George's County, said she expected 450 to enroll and instead had 485 students at last count. "The population boom is here," she said. School officials put the capacity of the building at 463, counting each kindergartener as half a student, and said that as of Sept. 30, the school was under capacity by 46 students.

But Acosta said that as of Thursday, she was still accepting more students, many of them immigrants who cannot speak English.

"We can't turn the kids away. We have a responsibility to teach them," she said.

To handle the extra students, Acosta received funding to hire more instructional assistants. But Acosta said the number of students is straining the school's resources.

"We just don't have enough space to carry out the instructional program," she said, frustration creeping into her voice.

Acosta has found herself answering to parents who expected the school to solve the crowding problem. "It's obvious to them that this wasn't the solution. I think we're all at a loss," she said.

In Montgomery County, the new Montgomery Blair High School, which replaced an old building, opened in the fall of 1998 with 2,755 students. That figure was under the 2,832 the school was designed to hold, but it also did not include an entire grade: 12th-graders were allowed to remain where they were. This year, with all grades enrolled, the school is just eight students below capacity. By next fall, when the new Blair enters its third year, the school will be over capacity at 2,958, according to the most recent projections.

Some planners say a full roster at a new school is more desirable than having classroom space unoccupied for years. "You'd be sitting with extra classes paid for with taxpayers' money and that would be difficult to explain politically," said David Boddy, director of facilities services for Virginia's Department of Education. Virginia school officials said they have had some schools open with more students than they were designed for, including Harper Park Middle School in Loudoun County that opened this fall, a year later than planned.

That's little comfort to parents who expect new schools to alleviate crowding rather than merely shift crowded situations to new quarters.

Cinda Haas, a member of a five-year-old lobbying group called Parents for Equitable Schools, has a third-grader and a fifth-grader at Dowell. "People say it's just a couple more desks, but it's not just that," she said. Her children get less time with their teachers, she said. And because there are five lunch periods to accommodate all the youngsters, her third-grade daughter has lunch at 1 p.m., five hours after the bus picks her up for school. Haas and other parents have gotten into the habit of sending bags of Goldfish crackers and other snacks to the school for students scheduled for late lunches.

Principal Alvestad said the school's large classrooms and wide hallways conceal most signs that the building is over capacity, though a small room that was listed on the architects' blueprint as a resource room instead became a regular classroom to reduce the sizes of other classes. Alvestad has hired two additional teachers to do one-on-one reading instruction with some of the students.

The crowding "is having no effect on instruction whatsoever," she said. "I can say that with total confidence."

Nevertheless, school officials spent the first three months of the school year scrambling to figure out why they under-projected. They concluded that it is difficult to forecast accurately the ups and downs of a fluid population like Calvert's. Planners estimate that each year, 450 to 600 new students will flood the county's 22 schools. For a school district of 14,928 students, that can be overwhelming.

"We're attracting students by droves," said school board member MacArthur Jones.

A year before Dowell opened, planners decided that the school should open with 656 students, 42 fewer than its state-rated capacity. Now the school has 728 students, 4.3 percent over what the state says the building can hold.

"The real problem is not so much that it is over capacity," said School Superintendent James R. Hook. "The problem is that we're over what we thought it was going to be. That's what parents are concerned about."

In response to complaints from parents, school officials have issued a report outlining the factors that fouled their planning. Among them: more transfers than expected, most of them from area private schools. But the one factor that made the biggest difference was that 89 students from Chesapeake Ranch Estates, once the oldest and largest gated community in Calvert, enrolled at Dowell, 23 more than the school district had planned.

Some students who were expected to remain at Appeal or Patuxent Elementary ended up at Dowell because of a provision that allows students to attend schools in the area near where their after-school babysitters live.

Hook is talking about adding mobile classrooms to the new school, which is awaiting completion of its playground and only recently opened its computer lab. He has even mentioned the one word parents most dread: redistricting. Nearly 1,000 Calvert elementary school students switched schools this fall under the redistricting plan, and Hook said the school district might have to redistrict again during the next three years if the population keeps growing.

CAPTION: At Dowell Elementary School in southern Calvert County, second-graders wait in a long line for their lunch. When it opened this fall, the new school already was over capacity.

CAPTION: First-graders Tyler Brown, left, and Brandon Mason listen to a story being read by their teacher, Marlin Stuart.