Your son must be your dependent, on your tax return, for you to claim a tuition credit.
In TurboTax (TT), enter at:
Federal Taxes Tab (Personal for H&B version)
Deductions & Credits
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If your son is your dependent, and your son or other relatives, paid additional tuition, or other qualified expenses (fees & books), you may include what they paid in calculating your tuition credit. There's even a loop hole available to claim the credit, if he is on scholarship.