The maximum tuition credit is $2500 and that's based on having only $4000 of qualified tuition and related expenses (you must be a half time or more undergrad). Only $1000 is refundable (the other $1500 only reduces your tax). For grad students, the max is $2000 based on $10K of expenses; none is refundable.
There's a new urban myth among college students that says they can get a $1000 from the government just for filing a tax form. For most of them, they simply aren't eligible. A full time unmarried student, under age 24, even if you don't qualify as a dependent, is only eligible for the refundable portion of the American Opportunity Credit if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. You usually must have actually paid tuition, not had it paid by scholarships & grants. It is usually best if the parent claims that credit.
You cannot claim a credit if you are, or can be, claimed as a dependent by someone else.