Yes, if you are a co-signer, and your child was your tax dependent in the year when the loan was made.
Further, you can continue to deduct the interest, if you pay it, for as long as the loan exists, even when your son is no longer your dependent, as long as he was your dependent when the loan was made.
And one more thing. If at some time it is more financially useful for your son to claim the loan interest on his return (such as your deduction is limited by your income), this is also allowed. You can treat the situation as if you made a money gift to him and he made the loan payments. (This is a special rule for student loans that does not apply to most other tax situations.)
