Loudoun students continued to show improvement on scores in the Stanford 9 achievement tests administered last fall compared with those of students nationally. School officials said the scores, released earlier this month, also showed that Loudoun is chiseling away at the achievement gap between white and minority students.

"Whether I take the long view or I look at this one year in comparison to last year, I feel good. We're on a positive trend," said Sharon D. Ackerman, assistant superintendent for instruction.

Students in Loudoun take Stanford 9 tests in the third through sixth grades and again in the eighth and ninth grades. The tests measure knowledge of general curriculum that education experts say students should know at specific grade levels. Although the tests are not crafted around Virginia's state curriculum, test questions are written by the same company that writes the Standards of Learning (SOL) exams and the two tests are similar, said Loudoun testing director Herbert Root.

Scores on the Stanford 9 are reported as percentiles, meaning, for instance, that a student who scores at the 50th percentile performed better than 50 percent of the students who took the test. Likewise, a student at the 90th percentile scored better than 90 percent of students who took the test nationally.

Over the past five years, the percentile ranking of Loudoun students has improved in all subjects and at all grade levels except the ninth grade, where scores have stayed steady.

Ackerman said scores tend to rise by just a percentile point or two each year, but the difference was still impressive because the scores of many students must improve to affect the percentile rankings for the whole system.

The scores also mirror Loudoun's results on Virginia's required SOL tests. The percentage of Loudoun students who pass their SOL tests has gone up each year since the exams were introduced in 1999.

Administrators said they have been particularly pleased with student's scores on Stanford 9 math tests. The percentile ranking of students in third grade has risen from 65 in 1998 to 72 this year. Scores have shown similar gains at other grade levels and across all ethnic groups.

"That certainly seems to be the most steady increase," Ackerman said. "Others have peaks and valleys -- that seems to be a dramatic incline."

Ackerman said administrators have analyzed math test scores and think a computer program students have been using in elementary school since 1999 may have helped with some of the improvements.

She said administrators were also pleased to see that the gap between the scores of white and minority students has been narrowing on most tests. In middle and high school, especially, the gap between the scores of black and white students on the Stanford 9 reading test has been closing.

Administrators said the Stanford 9 testing provides a helpful snapshot of how Loudoun students are doing compared with students in the entire country. Loudoun students take the tests in the fall, which often helps identify those who are in danger of failing their SOL tests in the spring.

County school officials are able to distribute page after page of data from the tests to schools, which can use them to target individual students for more work and subject areas where classes are weak.

"We have the capacity to take this data apart like we never have before," said Mary Morris, principal of Evergreen Mill Elementary School in Leesburg. For instance, Morris said, scores at Evergreen have been excellent -- but carefully analyzed data show teachers should work especially hard on teaching fractions, decimals and preparatory writing for essays. "We can get down to the nitty-gritty," she said.