At the beginning of every school year, an anxious waiting game plays out at school divisions' central administration offices, a kind of gambling in which big money and teachers' jobs are on the line.

Between the first day of school and Sept. 30, officials watch to see whether their projections of the division-wide student enrollment end up resembling reality.

The projections matter because the state gives money to local school systems based on the number of students enrolled. The more students who are enrolled, the more money a school gets from the state so that it can hire more teachers.

During most years, Prince William County's projections have been short of the "actual student membership." This year, Prince William school officials are saying their predictions were a little too high, for the first time since 1998..

For the 2005-06 school year, officials projected an enrollment of 69,021. Now, school planners are saying the actual enrollment is 200 to 800 fewer students.

If that bears out Friday, it would be the seventh time the division has over-projected its enrollment in 22 years, school officials said.

That means county schools might have to reduce state revenue projections, causing more schools to slash their budgets because they will not have the students to warrant the excess state aid.

Also, teachers who had planned on working at one school and perhaps bought a home nearby might be transferred to another school or take a different position altogether -- a process called "de-staffing."

School officials say de-staffing can happen even in the years when the division has more students than expected. There are some principals who, for various reasons, predict a large enrollment and hire more teachers than needed.

What distinguishes years of division-wide over-projections is that many more schools than usual will have to reconfigure their budgets and move teachers.

"Generally, we try to make an accurate projecting, and if possible, we would like to be low on the projection," said David Cline, director of the school system's financial services. "It's easier having more kids than projected because you'll have more schools that are winners than losers. You can hire more teachers. With fewer students [than expected], though, you've got make internal adjustments."

As of Sept. 6, the first day of school, there were about 65,200 students enrolled, far fewer than the projected 69,021. Enrollment always increases by a little more than 5 percent between the first day and Sept. 30. Many students miss the beginning of school because of vacations or other reasons, said David Beavers, a school system planning analyst.

Although planners say there could be as many as 800 fewer students than expected by Friday's count, it will most likely be about 300, Beavers said.

Cline, the financial services director, said that Virginia gives about $3,820 per student, so if the ultimate enrollment is 300 students fewer than projected, the school system's overall projected state revenue would be cut by more than $1 million. Because the student-to-teacher ratio is one to 24 or 25, about 12 teaching positions could be eliminated or changed to different jobs, he said.

No teacher, however, will be fired as a result of the process, Cline said.

Beavers said his office helps calculate a projected enrollment by tracking how housing developments proceed in the approval processes and construction phases.

"We put a lot of thought into it, so we get an idea of what might be coming in the next 12 months," he said. "But when it comes down to it, it depends on economics and how many people are buying homes and how many people are ready to move."

One reason the school system might have over-projected is that the number of building permits issued recently tapered off, he said.