@sophie2001,
As a last resort, just walk up behind him in the hallway, spin him around and before he can react plant a kiss on his lips. When finished, say "I've wanted to do that for the longest time," and walk away. I'm betting he asks you out within 24 hours.
PS: You may want to verify that there are no teachers around, as your school may have rules against this. Also, having a good lawyer helps since this could be considered an assault. But any red-blooded straight male would never file charges. lol
Ok, I'm just kidding about the above. In all seriousness, just ask him. Maybe he is shy and insecure around girls and would jump at the chance to go out with you. (This worked well for my wife back when we first met.)