I imagine that a lot of people are high in the college system. I read some stats a few years ago that said something like 1 in 7, but I know a lot of stoners.
It does seem that, when studying, it lets you just wrap yourself up into a ball and read for hours on end. In class, when i've had to give lectures on specific topics, I find that it really lets me punch up the stuff.
In class, I am usually distracted, because I take notes quickly, but, if I'm only a little high, i can just sustain my attention on the most boring thing.
As far as it effecting memory, I find little of that. I mean, if I'm high as a motherfucker, I will forget things and spend ten minutes looking for a lighter, but, when i'm sobered, my mind seems rested and I am able to recall tons of information. I also imagine that it decreases nervousness, which, if you think about it, sounds quite different than most paranoid responses to marijuana. If I smoke, I really don't worry about my behavior because i can remain extremely composed.
Bottom Line: there is nothing wrong with taking a small amount of marijuana (and it needn't be small, really, but enough to give you the strong effects lacking the crippling effects of being super-stoned) before going to school. But, really only in easy classes, because, if yoju have to be doing 20 things at once, you need a clean perspective.