What's wrong with him! It's been days—OK, a day—and he hasn't texted you back. What could he possibly be saying? Or, rather, implying, since obviously he's saying nothing....in text form, at least. Rest assured, he's probably not dead, unless you were hoping that's why he hadn't texted in the first place, in which case: shame on you! But it's more likely one of these reasons:
1. He hates you and everything about you. Was this your first text to him? Or your first 50 texts, all unanswered? Then it could be that he doesn't really want to communicate with you, on account of his not liking you. At all. It happens. Be glad he hasn't led you astray with texts that might give you reason to believe he can tolerate you when he really can't. Move on.
2. He doesn't know what to say. Um, yeah, 'cause boys are, uh, a bit on the brain-dead end of the emotional spectrum. Could be that your text so pleased him that it froze up the mechanism that connects his brain-talky-part with his thumb-tappy-parts. Expect him to blush when you see him next, perhaps during his next head-bangy-into-walls session.
3. He hasn't checked his phone. This can be particularly apt if his phone is too large to fit in his pocket, so he carries it in his backpack—the backpack that today he left at home. Thus explaining, too, why he's looking over your shoulder during class and seemingly oblivious to the way you're so seductively scratching your scalp with your pencil eraser.
4. He's playing games. No, not Angry Birds or that other game with what we assume are monkeys running at top speed, collecting bananas or something. He's playing games with your heart. One such game goes like this: You demonstrate interest in boy; boy likes you back, but has dumbass friends who tell him not to respond right away; boy listens to bad advice to "leave you hanging;" boy texts back when he thinks that if he waits any longer you'll no longer be interested; girl, excited to receive text, responds immediately; repeat. In reverse, this is infamously known as girls' "three-day rule." It's a lose-lose game for everyone involved. Better ask him directly if he likes games and then suggest a date night playing Risk.
5. He wants to reply with the perfect text. Some guys are thoughtful, cute, funny, and charming—but not one-hundred percent sure of themselves when it comes to texting girls. It's possible he's planning on the perfectly crafted Tweet-long message to send back to you, and needs a moment of quiet (i.e., a day and a night) to formulate it. Just don't wait for more than a day for your Shakespeare, or you'll likely to find yourself saddled with an insecure weirdo.
6. He’s dead.