This happened to me in English comp. I decided to make the most of the class by really studying style. I turned in three papers utilizing different author's styles in my own way: H.P. Lovecraft, Hunter S. Thompson, and Henry Thoreau. I learned a hell of a lot but was told that I cheated. I told them I would sit after class and write a paragraph or two of each style for them. They said it wasn't necessary as they could 'tell', and that since they couldn't prove I cheated, the highest I could get was a C.
I almost quit college over it. That aside, the amount of cheating in my engineering courses was high. There was only a 10% grad rate within 4 years and 16% total. I think it was the top 10% and cheaters that could graduate.
There certainly is such a thing as being too aggressive in trying to detect cheating. It happened to my dad once but he cleared it up by re-doing the problem from scratch in front of the teacher.
I think it's absolutely critical that any accusation of cheating allow the student to respond, preferably to a different teacher if the original teacher still thinks they were cheating.
I almost quit college over it. That aside, the amount of cheating in my engineering courses was high. There was only a 10% grad rate within 4 years and 16% total. I think it was the top 10% and cheaters that could graduate.