Gar-Field Senior High School has long had a good Advanced Placement (AP) program, with more than 400 of the college-level AP tests given every year. But that was not enough for Principal Roger Dallek and the school's faculty.

So they decided to introduce an even more demanding program, the International Baccalaureate (IB). This year, Gar-Field graduated its first class of IB students and doubled the number of college-level tests given at the school.

Connie Giorgio, the IB coordinator at Stonewall Jackson High School, whose own successful IB program has brought her school national attention, called the Gar-Field results "astounding." In just one year, Gar-Field has jumped to 20th in the United States and 35th in the world in the number of IB tests given, and its teachers say they plan to do more.

"Our teachers and students are now challenged to perform at their best, and the circle of academic excellence has widened," said Peggie Constantino, Gar-Field's IB coordinator. "We have over 800 students enrolled in the pre-IB and IB courses out of a population of 2,800 students. . . . We have an open enrollment policy in which any student willing to take on the challenge can enter the program."

Such encouragement for students, plus colleges' interest in AP and IB courses and Prince William County's unusual policy of paying many AP and IB test fees, has caused the number of college-level tests to increase 13 percent this year in county schools. In The Washington Post's annual Challenge Index list, a measure of AP and IB participation, Prince William's rating of 1.300 places it sixth out of 22 Washington area jurisdictions.

Two smaller school districts, Manassas and Manassas Park, which also pay the test fees, have college-level courses at their high schools. Osbourn High School in Manassas gave 239 AP tests and ranked 18th among area districts. Manassas Park High School gave 38 AP tests and had 41 tests in English and psychology under a long-standing program conducted at the high school. It ranked 13th among area districts in college-level test participation.

Part of the increase in Prince William has been a jump in the Challenge Index ratings for Osbourn Park High School, as well as increases for Gar-Field and Stonewall Jackson and a very strong AP year at the county's newest high school, Forest Park. A measure of Prince William's prominence on the Challenge Index list is that six of its eight high schools rated above 1.000, meaning they averaged more than one AP or IB test per graduating senior, a participation rate achieved by only about 5 percent of U.S. schools.

Constantino said the greatest obstacle in making such ambitious high school course schedules succeed "has been trying to balance the workload for students and teachers. They are all overachievers, and we work hard to keep them all balanced."

"Our IB teachers are also club sponsors and sit on numerous committees," she said. "The students are in all kinds of extracurricular activities, too, and they have so many talents that they have trouble balancing everything. . . . Flexibility is the name of our game."

Washington area participation in AP and IB programs, said by many experts to be a measure of how well schools are preparing students for college, soared again this year, giving the region possibly the heaviest concentration of college-level courses in the country. Washington area public schools gave 65,194 AP or IB tests in May, up 25 percent from 2001. Nationally, about 40 percent of U.S. schools do not offer AP or IB, but only one of 156 local schools, Ballou in the District, had no college-level tests this year.

The new emphasis on college-level courses stems from the courses' unexpected success in some inner-city schools and a 1999 U.S. Department of Education study by Clifford Adelman showing that students who take hard courses in high school, no matter how well they do, are more likely to finish college than students with good high school grades and test scores who skip the most demanding classes.

AP began in 1956 as a program for a few elite public and private high schools, where seniors and juniors were given college credit for some high-level courses so they would not be bored by having to cover the same material in college. Average and below-average high schools, such as East Los Angeles' Garfield High School as portrayed in the movie "Stand and Deliver," found the program helped their students too.

The IB started in 1968 as a high-level, standard curriculum for high schools around the world that catered to the children of diplomats and international business executives. In the United States, it is much smaller, with just 350 schools, than the AP program, with more than 13,000 schools. But it is growing, particularly in the Washington area, where there are 21 IB public schools.

Both AP and IB courses are taught by high school teachers who must prepare students for final exams written and scored by outside experts. A panel of the National Research Council recommended this year that AP and IB courses become deeper and more conceptual, and some private schools say their curricula are too restrictive, but no other programs have proved so popular in the last decade.

AP tests usually have 90 minutes of multiple choice questions and 90 minutes of essay questions or complex problem solving, which is graded by people, not computers. IB exams, which usually have all essay or problem-solving questions, can take as long as five hours.

Last May, 1,585,516 AP tests in 35 subjects were given to 937,951 students in the United States. That same month, 67,697 IB exams were given to 25,024 U.S. students.

AP is "by far the most successful and trusted high school program in America," said Peter Negoni, senior vice president for K-12 programs at the College Board, which created AP. "We believe that this program should be available to all children in this country."