For tuition, you can't claim tax credits for tuition unless you claim the child as a dependent. And you can't claim him as a dependent if he files a joint return with his spouse, regardless of any other conditions.
If you have a loan that was taken out while he was previously a dependent, you can continue to deduct the student loan interest on that loan even when the student is no longer a dependent. You must be a borrower or co-borrower (not a co-signer, that's different) and you must be the person who pays the interest. If the loan is only in your child's name but you make the payments, the child can take the student loan interest deduction on their tax return because they treat the payment as if it was a gift from you to them which they used to pay the loan.
