It's August and for 3,200 Prince William students, school finally is out.

Tomorrow marks the end of summer school for 1,450 county high school students, a bumper crop of summertime scholars. A week ago, 1,750 elementary and middle school students finished their studies.

Summer school is increasingly big business in Prince William -- so big that school officials say next summer they'll probably add a third school to those offering summer classes on the county's eastern end. For the second year in a row, the numbers have been 50 percent higher than predicted.

Long a holding pond for academic failures, summer school now attracts more and more students who want to get ahead by taking a course they won't have time for in the regular year.

"It's about 50-50," said Paul Tiscornia, principal at Osbourn Park High School, which along with Woodbridge, was open to ninth- to 12th-graders this summer.

Every student taking Algebra I at Osbourn Park is studying the subject for the first time, Tiscornia said.

At Woodbridge, more than a dozen students from Thomas Jefferson High School for Science and Technology came to take a computer science class.

Woodbridge was also the site for a special course for 40 academically talented elementary school children who studied paleontology, cinema and probability and statistics.

But most of the growth, school officials say, is because of a state subsidy that provides free tuition for students in the bottom of their classes.

Those who don't receive the subsidy pay $70 for each three-week semester of a high school course. A five-week elementary or middle school class is $80.

Finding teachers to fill all the summer school slots can sometimes be a challenge. The $3,720 salary for high school teachers and the $1,760 for elementary and middle school teachers is an incentive, but often a little arm-twisting is necessary.

When enrollments burgeoned at the last minute, Woodbridge principal Alan Ross said he spent several evenings on the phone rounding up extra teachers.

"I felt like an aluminum siding salesman," said Ross, recalling numerous calls trying to lure teachers back from vacations.

At Osbourn Park, Tiscornia said he'd been able to try out some teachers who have applied to teach there but have not yet been hired by the county. Some are now strong candidates to fill open positions, he said.

About 50 high school students served as aides in the elementary and middle schools, and Tommy Carter, who supervises summer school for the county, hopes some will decide to go into teaching.

Students compete for the $5 per hour aides' jobs, he said.

Summer school offers opportunities not just for students to get ahead, but also for teachers to try new things, its champions say.

"The teachers are learning as much as the kids are," Carter said.

The summer is a time to experiment with smaller classes and longer periods of time devoted to a single subject, he said. "It's not like regular school. We try to make it fun. There's a lot of hands-on and acting-out things for the children."

Many teachers are enthusiastic.

Walter Bailey, a 25-year veteran in the classroom who is finishing his first stint in summer school, said he's "tried a lot of things I've never had time to do" in his world history class.

"It's intense work, so concentrated. I think it would be wonderful if you could do a similar kind of thing during the year," Bailey said.

Bailey had 12 students first semester and 19 students second semester, which allowed for more free-wheeling discussion and more use of the library.

During their Shakespeare unit, a 12th-grade English class at Osbourn Park held a "trial" for the 11th-grade class, putting Macbeth in the dock for murder.

"He came out innocent," said Tiscornia.

The toughest thing about summer school, principals say, is enforcing the rigorous tardy policies, which mean no credit for students who miss more than 15 hours in six weeks. Teens think of many excuses for being late or absent. According to Ross, he encountered three girls who were coming in late once morning. "We've been in an accident, Mr. Ross," they told him.

Separate interviews with the girls revealed three different renditions -- different cars, drivers, circumstances.

"Afterwards, I thought, this is amazing. These girls have been in three different accidents and still managed to get here!" Ross said.