Rick's post is the general rule -- the "exit interview" works like the annual review at your job, except the program holds all the cards, because (a) they have no real incentive to offer a raise, and (b) if they reduce you, your options are severely limited.
It's important to investigate the program's/coach's reputations for handling these sorts of things before committing. Some are notorious for using big %'s to lure in freshmen, only to savage them come June so as to free up money for the next class. Others make it a point of honor that they don't reduce you unless you have engaged in misconduct.
The best way to avoid this fearful waiting game is to ask for a 4-year guarantee when your offer comes. This is now something the program CAN do per NCAA rules, but it doesn't HAVE TO do it. I advise any player, upon receiving an offer, to ask, "Would I get the 4-year guarantee with that?"
They may say no, but then at least you'd go in with your eyes wide open.
Then again, sometimes they say yes.
And sometimes, the response is, "If that's all you need to commit, then, DONE."