That all depends. If he is around his friends, then he will be harder to figure out what he is really doing. If your alone with him and no one is around, that's your best chance of figuring him out. Check his body language and see how what he is doing when he is with you. Look up some articles on the internet about body language and make mental notes when he is around about how he is positioned when your around. Also, notice how often you see him. If he is taking random routes to class so he can walk by you, or sits somewhere in class or at lunch or wherever you see him, if you can easily see him, he wants you to take notice of him and that he is around. At this point, he might be still trying to figure you out from a distance. If he is playing it cool, he will eventually get the point across that he is interested, just keep all lines of communication open. Verbally and visually. Hope that helps! There wasn't a whole lot of information to go off of but that should help a little.
if he's not interested, you'll know because his attention span is very short and he's ready to bail at another opportunity...for someone playing it cool they are just riding your wave and letting you initiate everything
A guy is uninterested when he doesn't have a lot to say to you and having to say "i have to go ttyl" and he never does get back to you.
He's playing it cool when he can't really get his words right; a lot of eye contact; catching his eye looking at you from time to time; always wanting to talk to you; talking about you to his friends is a major one too; and also seeming kinda nervous