I gave my students a take home exam over spring break. (This is normal where I teach) One of the questions was particulary difficult. It came down to a factor of three in the solution. That factor inexplicably appeared with no justification on many of their exams. I intend to have the students I suspect of cheating come to my office to solve the problem on the board. What would you do?
Edit: I gave them the Tuesday before spring break until the Thursday after. I didn't want it to be right before or right after.
When I say normal I mean giving take home exams.
That's a terrible thing to be considered normal. Those students were on break, on vacation. I didn't do work for my job when I was on vacation! I hate cheating, but I hate that you made them take an exam on break even more.
Edit: "Class, I see some of you did not understand the way I require work to be shown. For this reason, I will reteach my requirements. Those of you who did not understand will be given an opportunity to retake the exam."