To Approach or not To Approach?

Start a conversation about school, or a common interest. Built on that, if they conversation moves to another subject he is probably interested.

Just start saying hi to him when you see him, if he wouldn't just be weirded out. If you do, remember to smile and wave. Once you two have sorta gotten used to that, ask him an open-ended question about something you two have in common. Like if both of you are in fourth hour math with a teacher who's famous for liking guys better, ask him what he thinks of her girl-hatred.

Do stuff like that often and make friends with him, but still use body language to flirt: leaning towards him, biting your lips, eye contact, stuff like that.

Comment on something, a class you might share, a math problem you don't get, something he's good at, or maybe even his shoes or hair or something. Examples: "Did you understand such and such problem in class today?" (or maybe slip in an offer to help him with something that he's having trouble with)

Find the time to try and talk to him, if you guys talk long enough you can tell if he likes you.
if nothing else make up some reason to talk to him. If he likes you he will then start making up reasons to his friends to talk to you.

What's wrong with popular people, they can't help it if they have a lot of friends and are in after school activities. But I think you should start hanging out with them, show up at the games and sit next to him in one of your classes. Make sure your always smiling and wear something really cute, show off your legs. That always works for me. Good Luck!