It is quite possible that you are receiving the Lifetime Learning Credit. This credit has an annual limit of $2,000.00 and is not refundable. It does not necessarily increase the amount of your Tax Return it reduces the amount of your Tax Liability. This is probably why you do not see this credit translating into a larger refund.
There is an income limitation to the Lifetime Learning Credit. If your MAGI is $131,000 or more (married filing jointly) or $65,000 or more (single, head of household, or qualifying widow(er), you cannot use this credit.