Summer school.

The words conjure up a vision of dejected youngsters slouched behind desks in half-empty classrooms-- trying to make up school work from the previous year.

But in Fairfax County summer classes are overflowing with 10,876 students, including 1,200 foreign-born students who eagerly -- and voluntarily -- have enrolled in English as a Second Language (ESL) classes.

Some of the county's unhappiest children this summer are non-English speaking students who trieid to register after the summer deadline passed and must spend the summer out of school.

One such child was Dini Djalal, the 9-year-old daughter of Indonesian diplomats.When Dini and her family arrived in Fairfax County last September, she was unable to speak more than a few words of English.

In May, Dinii startled her classmates by winning Chesterbrook Elementary School's fourth grade spelling championship.

"I read a lot of books and I look up words I don'tknow," Dini explained last week, when asked the secret of her success.

Dini and her parents were in Disney World during summer school registration last month. When she visitedWoodburn Elementary School -- one of several summer ESL centers -- last week, Dini sulked about being excluded from summer school and complained that her vacation would be "boring."

Dini was lucky, however. That morning ESL director Esther Eisenhower found a rare vacancy in the program, and Dini was dully enrolled.

Dini's scholastic success is repeated with slight variations across the county.

ESL teacherscite case after case were students who a year ago spoke no Englsih have now moved out of ESL, into the academic mainstream and to the head of their classes with lightning speed.

Legendary in Fairfax County education circles are two former ESL students. One, a student who spoke no English in 1978, is attending the Massachusetts Institute of Technology (MIT) this fall and the other, a Spanaish-speaking student, was the first ESL student elected president of a high school student council.

"They do remarkably well -- in fact, it'samazing," said Woodburn principal Alex D. Wargo.

"They really want to learn," adds Linda Cotts, an ESL teacher at Falls Church High School. "They spend hours on their homework and they're being encouraged by their parents to do well."

Many ESL students say they want to go to summer school to retain their newly acquired English over the summer months.

At Oakton High School, 15-year-old Thuy Le is working on her English -- which was good enough last year to help her earn five As and one B. Although she is a member of the National Honor Society, Thuy says her English pronunciation needs some work.

"My younger brothers and sisters learn so much faster than me," she says.

Like many other ESL students, Thuy spends much of her spare time in the local library -- which is well-stocked with books and periodicals in her native language, Vietnamese.

A few miles away at Lake Braddock Secondary School, 19-year-old Hai Van Nguyen, a Vietnamese refugee who spent five months in a camp in Malaysia, studies English in a regular high school class. Hai says he is enrolled in summer school, even though he would like to havea summer job, because he wants to graduate with his class next June.

And at seven o'clock each weekday morning 11-year-old In Shik Chang boards a yellow bus which takes him to classes at Woodburn. In Shik is a sixth grader who came to the United States from Korea seven years ago.

He now speaks nearly flawless English; he is a regular on the honor roll, and he was elected vice president of his elementary school this year.

Why then, is he attending summer school?

"To help out with the little kids in the kindergarden," he explains.

A teacher says In Shik is not unusual.

"Many of the older kids like to come back to ESL to help the newcomers."