I used to smoke tons when I was in college. I would wake and bake every day, then toke up before I went to class in the afternoon. It's really a matter of individual tolerance; some people might get high and laugh their ass off at something, leading to a pissed off professor and, god forbid, getting kicked out of class.

I've always held off from getting too stoned, but it is nice to sit in class, and being high helps you to get comfortable and interested in the subject. I've taken tests high before, but only if it was for a bullshit course; for example, I toked before my psychology and anthropology finals, but I wouldn't do it before a math or science test, which would be fucking moronic.

The idea is to know your limits, and not do any harm to your academic reputation or act like a moron. If you can do that, there's really no reason you can't smoke a J before class. Just remember some visine and mouthwash.