Alexandria's T.C. Williams High School, one of the largest and most diverse schools in the region, has begun to see a significant increase in the number of college-level tests its students take.

T.C. Williams Principal John Porter last week reported a 50 percent increase in the number of Advanced Placement (AP) tests given at the school in May. The tests are given at the end of college-level courses in several subjects. Many educators consider them important in preparing students for university work, but each test can cost as much as $76, and many AP students decline to take them.

In recent years, T.C. Williams has lagged behind neighboring high schools in AP test-taking. Its total number of tests dropped from 324 in 1996 to 321 in 1997, then to only 286 in 1998. This year that trend reversed, with 402 tests given to 200 students in 19 subjects.

Alexandria School Superintendent Herbert Berg said the effort to get more students to take AP tests follows efforts to encourage the taking of other college-related tests, such as the PSAT and SAT. "I like my kids to take those exams," Berg said. "I think they help kids prepare for college."

A recent study by Clifford Adelman, a senior research analyst in the U.S. Education Department, shows that a strong high school program full of classes such as AP courses is a better predictor of college success than test scores, grades or class rank. Although the AP tests, written and graded by outside experts, are rarely required, AP teachers say that students who take the test usually learn more about both the subject and the analytical demands of a college examination. Adelman and several other educators have said it is better for a student to take and fail an AP test than not take it at all.

In a recent survey of 1998 AP test-taking by The Washington Post, T.C. Williams ranked 77th out of 139 Washington area schools on the Challenge Index--a number calculated by dividing a school's total number of AP tests by the size of the graduating senior class. T.C. Williams's Challenge Index rating was 0.529 in 1998, compared with 0.985 for Arlington's Wakefield High, which, like T.C. Williams, has a large number of disadvantaged students. T.C. Williams's 1999 rating is 0.685.

Wakefield is much smaller than T.C. Williams but has a comparable portion of low-income students (41 percent at Wakefield and 31 percent at T.C. Williams) and of seniors enrolling in four-year colleges (61 percent at Wakefield and 52 percent at T.C. Williams.)

Interviews with educators at both schools suggest that Wakefield students receive strong encouragement to take the tests, while T.C. Williams teachers have often let students make up their own minds. In 1998, 71 percent of Wakefield students in AP classes took at least one AP test, while only 31 percent of T.C. Williams AP students did so.

Even if a student is struggling in an AP course, "we would encourage them to take the test anyway, because the very experience of taking the exam is useful to them," said Wakefield Principal Marie Shiels-Djouadi.

"You never know what a student is capable of achieving until you put that challenge in front of them," said Mike Grill, who teaches Wakefield courses in AP American history and European history.

Wakefield's emphasis on students taking the test results in a lower percentage of AP passing scores--41 percent at Wakefield this year, compared with 71 percent at T.C. Williams. Arlington AP students get an extra grade point in their course grade, and Alexandria AP students get an extra half point whether they take the test or not.

Fairfax County high schools' passing rates dropped this year when their School Board became one of the first in the country to pay all AP test fees and require that AP students take the tests, but many Fairfax teachers said they were still happy to give more students a close look at what they will face in college.

Former Arlington school superintendent Arthur Gosling suggested requiring AP tests and paying for them three years ago, but so far the county School Board has not taken action. Berg said Alexandria officials have discussed requiring the tests but have made no decisions.

Some AP teachers at T.C. Williams said they would like to adopt the Fairfax system.

"I think they should be made to take the test if they are taking the course, but the School Board doesn't want to hear that," said Rebecca Buckbee, who teaches AP English at the Alexandria school. "I tell them, 'If you read everything you are supposed to read and don't depend on Cliff Notes . . . you will have no problem with the AP exam.' "

She and Patrick Welsh, the other AP English teacher at the school, said their lessons are full of questions from previous AP tests. "We are very closely aligned to what is on the exam," Buckbee said, "so I don't think they miss too much of the college-test experience if they don't take the actual AP test."