Ok I'm 14 and sort of stuck in the same situation as you but I still have a few things for you to try...
1: Make sure you've seen how he acts around certain people and how he also acts twards you around those people

2: If you think you have seen as much as you can see about him from his actions and personality around others and you are comfortable with approaching him then just start with a simple smile if he looks at you (especial if you catch him staring...trust me he will eventualy)make sure one of your friends says your name when hes around like calls you over to them or something so that he knows your name (that is if he doesn't know it already).

3: Express your personality around him. Make sure that he knows your personality so that you both have a look at one anothers personality other wise you may both become socialy awkward around one another and if that happens things might go down hill.

4: Once he starts noticing you make sure not to be to obviouse about what you think about him or that...is how you feel about him. Like don't stare at him constantly or laugh at EVERY SINGLE one of his jokes. Sort of smile when you laugh at one of his jokes though and make sure that other people are laughing as well.

A Quick Trick To Get Him Looking At You: Use loli-pops. I know it's an old trick but it still works. twirle the loli-pop in your mouth but make sure hes looking when you do so. You can also try putting your pencil in ur mouth and act like you are looking through papers as you do so. but dont like GRIP it in your mouth...it sounds gross but it works I do it all the time and it really gets him looking. While you're sitting at your desk point your legs in his direction and try one of the tricks that I just mentioned while you are pointing your legs tward him.
That's all I have and I really hope it helps you...oh and I'm going to throw this in as well...

Just because you dont think he likes you because you think you aren't pretty or something...well just because you may not seem pretty to other people..er...what ever...doesn't mean that he doesn't like you...I'm not all that pretty myself but I know two hott guys that like me...how I know this is they I catch them staring at my legs...they smile when I laugh...they look at me when they are goofing around with one of their buddies and they don't give me the "blech" kind of look when I laugh or smile at them when I catch them staring.
OK so again...hope this helped...it should...and if he doesn't accept you for who you are then trust me...he's not worth your time.:)