I got this little seed of an idea in my head, and I can't seem to make it grow. Yet.

Here's the pitch: It's Harry Potter meets Saved by the Bell: The College Years.

Let's say,  You're a sorcerer in some generic 18/19th century euro-themed area.  You, like all youths of a magical inclination, have gone through a long, anti-social magic home-schooling with your local lunatic wizard. Suddenly, you turn 17.  Your apprenticeship is over; it's time for college.  By some skill, or luck, or family connections, you've gotten accepted to a rather obscure sorcerous college. In a way, it's kind of relieving. That old wizard Batnose or whatever, isn't breathing down your neck all the time anymore.  You can go out at night, make-out with people, play drinking games, or just have a semi-normal social life.  But first, your have to make some friends.  Will you survive the cutthroat social climate of college?  Will it change you for the better, or worse?

So, I made that all up on the spot, but I think it conveys a bit about what I'm trying to achieve.  The point is, your character is a young, liberated magical youth.  It will be a game of social exploration/survival. You have a blank-slate to explore who you are, and who your friends are.  It's a game about peer pressure, fitting in, hard decisions, sticking to your guns (or wand), and making friends.

The thing I want to stress with the mechanics is that your character is largely a measure of what people think of you.  I imagine characters to have a few immutable qualities about them, while the rest is a constantly shifting rep and expectation.
For instance "Johan Archimedes the 26th really is oddly likable, quiet, and has a good memory, but most people also think he's a slacker, sexual-archwizard, and bad at rune-carving." The traits, and repuations, function nearly the same in conflic resolution, but interact with stakes and rewards in different ways.  To reinforce the "this isn't you, it's what people think of you" avenue, I'd like a character's advancment, or change, to occur largely at the behest of the other players.  Johan's player didn't choose to be a sexual-archwizard, he was given that rep.  Players can choose to play into, or against their rep, with some influence over the advancment, but these things get attributed to you, not by you. Stakes and outcomes of resolutions could either be narritive goals, rep, or hopefully both.  Anyways, it's pretty fuzzy, but I have about a million ideas around this game.  In addition to general input and encouragement (hopefully) I have a few guiding questions.

1: I'm still struggling with how to make this meaty enough to drive play.  Why will the players really care what people think of their characters, versus what there character really are, or the player's vision of them, or how they grow up?  I know it's somewhere in there with the immutable traits, and the attributed ones, and the interplay between them, but it's hard to put my finger on it.

2: Moreover, how do you make the other players care?  I want people to feed on each other's character's stories, and invest some creativity into furthering them? I just can't quite figure out how to prompt that.

3: Do you think this kind of idea would benefit from some sort of strict pacing and/or endgame? Like semester by semester till you graduate, or something like that?  I was thinking about have it so magic doesn't really affect your rep that much.  Like, it's easy to make a love-potion, but hard to go on a good date kind of thing.  With the pacing semester by semester, characters could just steadily get better at magical things, making it easier to get your narrative goals, but harder to grow into the Thing You Want.  It would also give a clear picture of how college changed you.  Like, with a MLWM type epilogue about the person you grew into.

Anyways, thanks very much for reading all that.

I'm actually working on something of a similar concept, although with different Color and a radically different Setting, called American Wizards.

Now, I've figured out the basic thematic premise of it (which is what is actually similar between your idea and mine; the fact that they're wizards doesn't actually have much to do with it) and how it applies to play.  It all breaks down to this stuff:

1.  The PCs have long-term goals.  The big 3 in my game are power, mastery, and artistry, but there's little "twigs" branching off of each.  But, anyway, point is, they have goals, and there are obstacles to these goals that they must address, or else give up on their goals.
2.  The PCs are young and inexperienced, not to mention engaged in learning a mysterious and dangerous art, so they screw up from time to time.  This causes unpleasant consequences that must then be dealt with.
3.  The PCs are part of a large, complex, and above all mercurial social group (a college), which makes relationships, popularity, and positioning very important.  Oh, and the PCs all have some manner of relationships to eachother.

All three of those have ramifications on each other; f'rinstance, making mistakes puts a hurt on achieving your goals, and can affect relationships (and making mistakes with regard to relationships, oh my; drama GOLD).  All you need is to create PCs that match those definitions, have mechanics and someone in a GMish role make sure those three things matter and aren't easy to deal with, and leave all PC decisions up to the player.  BAM.  There's your game.  I don't see a need to enforce pacing or endgame at all.

-Marshall

Oh, and, I hope you're not discouraged by the fact that I'm already working on a similar game, 'cause you shouldn't be.
I mean, you're not going to invent flour, and if you try then you're doomed to failure; your responsibility as a designer (or any other sort of artist/creator thing) is to, say, bake a damned good apple pie.  And it doesn't matter that I'm also making an applie pie; there's lots of ways to make damned good apple pies.

Hi!
  Maybe make a bar where one end of the bar say +/-5 and it has their identity and the other end of the bar says +/-5 and it has their rep (determined by other people). And their role is modified accordingly based on where they are on this track. So if there are on slot +/-3 for their identity and they need to resolve a conflict, the would get +3 when acting according to their Identity and -3 when acting according to their rep. Then after the conflict is resolved it either moves closer to Identity or Rep.
  And every character has 2-4 of these bars, for example:
Harry Porter:
Powerful<-----"+/-1"------>Normal
Gloryhound<-"+/-4"--------->Unremarkable
Stupid<-------"+/-2"--->Quick thinking
  So, when Harry wants to do something unremarkable (like go to a Quidditch match) he'll get -4 because he is so famous...
  Does that make sense?
  Does that help?
  Good luck man!

Have you ever heard of "Pantie Explosion"? Look up the review on rpg.net, because it's mechanics seem perfect for what you're doing, in that it's a game about peer pressure and school hijinx, but centered around supernaturally powered characters. (The name is a joke. It's meant to be a bad Japanese translation.)