I'd ask the teacher to please contact me should that kind of thing happen again, and maybe check into what the schools policy is on that.
But honestly it sounds like the term "cheating" is new to your ds and he didn't really realize what he did was wrong. I'd probably focus more on making sure he knows what is considered cheating and make sure he knows that dishonesty is never a good thing. Although it seems weird that she had the answers on the board while tests were on desks anyway
But to me it seems like being really upset and dolling out punishment wouldn't be the most uplifting thing, and unnecessary, if he didn't realize at the time that it is cheating.
~starting to receive squares and just want to say THANK YOU~ to all you awesome mamas!~