First of all, you need to tell your son's father that if he needs anything financial, he is to talk to you directly. Your son has no business being in the middle of your financial issues.

Whether or not he can claim your son on the taxes all depends on your court order. If it isn't addressed at all and you are the custodial parent, you get the exemption.

One thing your husband may be trying to do is claim that what he is paying is child support so that he doesn't have to pay the court ordered child support.

Personally, I would go to court and get the status quo (him paying a portion of the private school tuition) as part of the court order.