Cheating

Today at lunch I got a call from my oldest sons teacher and was informed that he was caught cheating on a test.  He is a straight A student so I am not sure as to the reason he would feel the need to cheat. I was informed that because of this 0 on his test, that he would not really recover grade wise. That his A would now become an F for the quarter. For ONE test?? Anyone else think that is a bit extreme? I think they are putting way too much weight on the tests then they should. Which means that he will have a really hard time getting his grade back up to an A at all. I dont quite understand why he would feel the need to cheat, especially considering its in a subject that he knows! I dont know how to handle it yet, as I have never had to worry about him doing something like this. How would you handle it if it was your kid?