Or, you could just explain that he needs to be sure, then if he insists it's child support, go with child support. If it's not, you'll find out, and be sure to charge for reading the five-page letter from IRS. And charge to check the IRS calculations. Maybe just do an amended return to be sure IRS considered everything. Yes, I'm being a little facetious, but if he's telling you wrong, he's sure to get caught cause she's deducting it and providing his name and SSN, so I might just take lay low on this one and let the agony of defeat run its course.