One thing I’m wondering about, if father no longer supports son after high school graduation (child support ceases), he can still claim him as a dependent?
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He would not declare him as a dependent necessarily, though divorced parents can make private arrangements between g thyHe selves as to who gets the child as a dependent Regardless of who is supporting the child. But some of the credits and deductions can be split using Form 8332 and the consent of the custodial parent. It appears OP is familiar with use of this form.
OP and Ex should decide who can best use the deductions that come with a dependent child in college, including the AOTC. If the dad can get more of a financial benefit and is willing to give the prized refundable tax credits to the OP, and OP’s tax situation is such that she cannot get those $s back, absolutely, she should work out something with her ex, at least for this year and see how it goes.