For the approximately 11,500 students and 500 teachers involved in summer school programs in Northern Virginia, summer means homework, busy work and up to 5 1/2 hours per day of classroom work over a period of several weeks beginning in late June and ending in early August. And for the students, there is the nagging knowledge that their friends are out in the sunshine swimming or at work earning money.

Students attend summer school because they have to repeat a course they failed or because they want to take a course they might not get to take during the regular school year. Teachers work in summer school mainly for extra pay - in Arlington, $8.05 to $8.60 an hour, and in Fairfax, a per diem rate based on regular contract pay. In Alexandria teachers get either one-sixth or one-twelfth of their regular pay, depending upon summer teaching schedules.

Students who are repeating a course say that in many cases the actual summer work is easier than during the regular school year. Their teachers often agree. But both groups agree that the concentrated hours of summer school classes challenge their attention span.

"The hours in class are too long to learn," moans one Jefferson High School students who failed English and history last year as a junior and is spending five hours a day making the work up at Oakton High School. Though he is passing, he says, "I never want to have to go to summer school again!"

"Summer school is easier, there's no question about that," says Ann Hughes of Robinson Secondary School, who is teaching English at Oakton this summer. "We put the course objectives in the hands of the students so they can see exactly what they to do to pass. The student works to those objectives and, for the most part, he does what he likes on his level.

"The work's easier, but I have no reservations about failing a kid who doesn't work. I tell them, 'Your body in class doesn't guarantee that you'll pass.' "

Sitting on the floor of an empty Oakton High School corridor, a notebook in her lap and a dictionary beside her, Sonia Aldes, 18, is confident she will pass her summer government class. She was unable to graduate in June with the Oakton High School senior class because she failed government during the regular school year.

"When I told my friends I wasn't graduating with them, they all said, 'Are you kidding?' "Aldes recalls. "My parents were very disappointed. I was so mad at myself for flunking.

"It's going fine now. It's easy. It wasn't hard during the regular school year really. I'm just sorry I didn't work harder then."

"It was depressing not being able to go through the traditional graduation," says Laurie Reid, 17, who missed June graduation at Stuart High School partly because she failed one grading period of English last year. "I just didn't go to class, so I failed. Now the work seems easy. But I don't really have any regrets. I think I've learned from these experiences.

Aldes and Reid hope to be among the summer school graduates in August. "They have a ceremony for us and everything," Aldes says.

A veteran summer school teacher, Clint Hannah, watches his typing class clack through part of its five days. The class consists of 11 "new" students - students who never had typing before and chose to take it in summer school - and seven "repeaters" - students who failed during the regular school year and who put in 2 1/2 hours daily in the summer.

"I get some of my best work in the summer," says Hannah, who teaches at Madison High School during the regular school year. "It's a more relaxed situation and there's more time without interruptions. In the winter, by the time I take roll, explain a few things and make an assignment, there's not as much time to actually type as there should be."

This summer Fairfax County is conducting three courses - a computer seminar, archaeology and field research in environment program." The courses are not available in every school during the school year and are available to limited number of students during the summer.

Computer seminar teacher Jerry Berry explains "the sequential axis" to a class of 15 attentive students who paid $98 apiece to take the course. They do not receive a grade, but they do receive a course credit toward graduation.

Tim Platt, 16, who will be a senior this fall at Herndon High School, paid the course fee himself in hopes that the class "will help me get a better job than the one I have now (pumping gas)."

"You have to be interested in computers to be in here," Platt says, "because this course takes up a lot of your summer." Platt estimates he puts in two hours of work daily outside of class on his own.

Students in the seminar spend about an hour a day working on one of three available computer terminals. Peter Hammer, 17, who also will be senior at Herndon High this fall, uses much of his computer time working on a "program where I'm trying to simulate Newton's gravitational laws and converting if from Basic (computer language) to Fortran (another computer language)."

"We're well taken care of in this class," Hammer says. "We get more attention in the summer than in the regular school year."