You need to ASK your dad if he claimed you as a dependent. He could still do it, and if his return hits the IRS first then yours will be flagged if you don't state you were claimed as a dependent. Divorced parents do this all the time to each other... one claims them without telling the other, then the other files... and the IRS has a fit and reject the 2nd parent's claim.
I don't think that school has anything to do with whether or not someone can claim you as a dependent. Generally, anytime you are paying more than 50% of the costs to support someone (MOTHER, FATHER, GRANDPARENT who is likely NOT in school hence SCHOOL has nothing to do with claiming someone as a dependent...) then you can claim that. So ask your dad what he did.
Look at your paystub. If you had any Federal things taken out for 2010, you should file. Even if you didn't make much, you can get what you paid back.