CHAPEL HILL -- Four students from Chapel Hill High School were suspended after allegations of cheating, but administrators believe it was an isolated event.

"The unfortunate incident that occurred recently at Chapel Hill High School should not be construed as a widespread problem but rather an event that occurred in isolation," said Stephanie Knott, the school system's spokeswoman. "Despite student allegations about events that may have transpired in previous school years, the school and the district have been unable to uncover any evidence that they actually took place."

Administrators believe at least one student used a copy of a master key to get inside the school and get answers to a mid-term exam. Knott said students claim the key has been passed from class to class over the years, but she said there is no proof to support the claims.

"I think, at this point, if students have graduated, there's probably little that could be done about it," Knott said, adding that security cameras led to the discovery. "The students involved have, according to board policy, taken a [grade of] zero for the test in question, and board policy does dictate for instances of cheating, out of school suspension."

Gregory Cizek, an education professor at UNC Chapel Hill, said hearing about the allegations gave him a sense of déjà vu. He wrote a book about cheating after running into a similar situation in Ohio a decade ago.

"There were a total of three tests that had identical scores and word-for-word identical answers to essay questions," Cizek recalled. "It turned out that students had broken into my office, taken copies of the final exam in advance of the final, made copies of it, written out their answers ahead of time, and then substituted the completed pages for the essay in the test booklet I passed out in class."

Now Cizek teaches test administrators how to handle similar situations.

"It's far better to prevent cheating than it is trying to detect it or respond to it," he said. "You can improve your own security so that you keep track of keys or access cards or test materials or things like that. Keeping test materials in secured locations that have their own system of locks and security is much better."

He said students are developing more and more sophisticated ways of cheating.

"[Writing] answers on your hand or on a piece of paper is pretty low-tech," Cizek said. "It's much more about cell phones, even small video cameras, pictures, communication with calculators, there are all kinds of ways in which cheating happens now in a testing situation."

Knott said administrators at Chapel Hill High School have already started changing locks. She said administrators have not ruled out asking police to get involved, but so far they're handling the investigation internally.