The two investigations into test irregularities that have rocked the Roanoke and Montgomery County school systems in recent weeks are a reminder that illegally manipulating standardized tests is more common that parents and educators would like to believe, according to testing experts.

"It's unfortunately common," said Gregory Cizek, a professor of educational measurement at the University of North Carolina Chapel Hill. "While by far the majority of educators across the United States are doing it the right way, there are some people who are cutting corners, like in any profession."

With so much of a school's reputation hanging on these tests, it's to be expected that some administrators attempt to nudge the odds in their favor in inappropriate ways, particularly since the passage of the No Child Left Behind Act in 2002, researchers say. In response, some state and local school officials are looking for ways to tighten security around tests and to close loopholes that unscrupulous administrators, teachers or students could exploit.

Although firm numbers on cheating nationwide are hard to come by, Cizek said anecdotal evidence suggests tests are being manipulated more often than reported.

"There's really no incentive for anybody to identify this and to vigorously pursue it. It often flies under the radar," he said. "If people blow the whistle on it, nobody's happy."

In Virginia, which tests about 1 million children every year, education officials have received 65 reports of possible improprieties over the past four years, said Charles Pyle, a spokesman for the Virginia Department of Education.

"I think that speaks well of the teachers, the administrators and the other school division employees who are responsible for making this work," he said. "In any human endeavour there will be individuals whose actions can be called into question and whose motivations can be called into question."

The pressure has gotten more intense since the No Child Left Behind law cemented standardized tests as the main measure of a school and school district's success, researchers say. In Virginia, that means that the fate of schools and, in some cases, the jobs of administrators rest on Standards of Learning tests.

That has led to an increase in reported cases of cheating, said Walter Haney, a professor at the Lynch School of Education at Boston College.

"It has become much worse and much more problematic since No Child Left Behind," he said. "The high-stakes tests are used not only to make decisions about kids but to make decisions about schools."

Over the past two months, anonymous whistle-blowers alerted the Virginia Department of Education that some students at Roanoke's William Fleming High School and at Montgomery County's Eastern Montgomery High School may have been inappropriately kept out of tests as a way to artificially boost pass rates.

A state report in the Fleming case pointed the finger at Principal Susan Willis and four other administrators. State investigators are still working on a report in the Montgomery County case, although local officials say they have no evidence that anybody did anything wrong.

"I think it's really a shame that the consequences have become so high and the stress on administrators has become so high that people would consider doing that," said Ben Williams, testing coordinator for the Roanoke County school system, which has not been accused of any infractions.

Although the state department of education has very stringent rules on how to administer tests and how to report the results, Williams said Roanoke County will beef up its own monitoring to check that students enrolled in certain high school courses actually take the corresponding SOL tests.

Officials have done these checks occasionally in the past, but now they plan on checking "as a matter of procedure," Williams said.

"That's new and that's in reaction to what happened in the city," he said.

It helps too, he said, to have proper training programs in place, as well as "a culture that doesn't accept people trying to circumvent the rules."

State administrators are also discussing using student identification codes to match students enrolled in courses and those who are sitting for end-of-course SOL test, Pyle said. The department started assigning high school students individual codes about five years ago as a way to better measure graduation rates.

"There would be the potential of doing the kind of post-check that would serve to keep everyone on their toes," he said, adding that this type of auditing is not "right around the corner."

In the end, state and local officials say, there will always be a way for unscrupulous people to cheat on a test.

"You trust people as professionals to do their jobs correctly," said Carol Jennings, Montgomery County's testing coordinator.

Staff writer Anna Mallory contributed to this report.