In our state the only thing that matters when calculation child support is how many children there are and what the noncustodial parent makes. They don’t care if the child is in day care or privet school. They don’t care about back to school supplies or sports. That’s what child support is for.

Now if the parents decide something and decide they want to split the cost that’s fine but out state does not standardly order parents to pay for extra things like that and if they do it’s a different matter than child support. So if child support is 500 a month and then they order a parent to split the cost of privet school that is a different bill. Child support remains 500 a month.

 Now at the time of a divorce a court is more likely to order the parents split the cost of privet school if the child has already been enrolled but they aren’t likely to come back years later and demand the split unless a parent can provide A LOT of reason for the change.

I think generally, CS is supposed to be related to relative income levels and those issues in state calculators.  However, if there has been a precedence of private school.. it's possible that the judge would order it to continue.. unless there was a big change in ability to pay.  and I would think both parents would be on the hook.. and possibly if the child is withdrawn from the private school.. then the amount towards that wouldn't need to be paid.. but of course.. the CO should spell that out.

My son attended private and public schools.  Tuition was never factored into the CS amount.  CS was based strictly on our incomes 

It is possible. I know that daycare is considered and if SD has been at this school for more than this year.... Yeah... there is a chance. It is all about the wellness of the child... blah...

I would think the public school would likely test SD before placing her as a freshman next school year. She's been going to this very small private school for years. While a number of years ago the school she is in advanced her a grade ahead, the kid is obviously not performing up to par. Her grade, in math for example, is in the toilet. 

The pubic school may recommend she start back at current grade (middle school) and play catch up. That too may set BM off. But why keep paying for the  private setting which doesn't seem to be benefiting the kid's education. It's been too long (under our old account) that I don't recall exact details on how your DH did the private school pay along with CS. He paid the school direct and also sent BM some monthly CS. So CS monthly would being paid monthly to BM doesn't reflect the private school payment. 

Daycare (which SD is now too old for, but this summer BM paid for aka summer camp) and heath insurance (which BM also provides) are the two factors in 'credits' calculated along with both BM's and your DH's income in your state. Your DH and BM make and have made so many off the 'record' out of court self agreements between themselves , they may by now managed to set precedence unless some new circumstance.