An interesting method by which I found out that people were cheating on my final exam.
I use different versions of midterm examinations to discourage cheating in my population biology class (~200 students). When the course started, I used to do the same thing for the final exam, but it was a little more complicated, because the final exam is administered by the registrar’s office, not by me and my teaching team.
At some point, somebody advised me not to bother with versions: the registrar’s office is supposed to be professional about administration, and they usually mix people who are taking different exams in the same room, so I stopped bothering with different versions for the final exam for a year or two. I do it again now, and you’ll see why.
In the year in question, my exam was given in two separate medium-sized rooms. My class was alone in these two rooms. I received a report from the invigilators in Room 1 about suspicious behaviour. They had warned a couple of students for acting strangely, and then warned them again. They weren’t prepared to say that they were sure that the students were cheating, but wanted me to compare their answer slates. In retrospect, they should have left the students alone until they were ready to sign a complaint against them (or until they had cheated enough to have it proved against them).