It depends on how much income he has and the source of that income and his age.
It sounds like the $16,400 deduction got his taxable income to 0. So a tax credit would do him no good.
Generally, students under 24 are not eligible for the refundable portion (up to $1000) of the American Opportunity Credit.*
* 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.
You may be missing out on the $2500 AOC plus the $500 dependent credit so that he can claim the $1800 recovery rebate credit.
Under the CARES Act, if a person is claimed, or qualified to be claimed, as a dependent on someone else’s 2019 return he did not receive a stimulus check, in 2020. If he qualified as a dependent for 2019, but will not be for 2020, he will get it in 2021, when he files a 2020 tax return.
Note that the requirement is not just whether he is actually claimed as a dependent, it's whether he qualifies to be claimed as a dependent.
