HRZ, the poster has already been advised to talk to the school district about their requirements. I think you may rest assured that the school district will tell them what their policy is with regards to tuition. I don't see anything in the original post that says that the primary issue is whether or not he will have to pay tuition. In fact, I don't see that it was even a matter of concern for the OP.
Now, if I may get back to what I was attempting to go into without being interrupted by irrelevancies, OP, I work in Employee Benefits and we occasionally have an employee looking to add a minor to their health insurance for just the reason you propose; the parents are having to re-locate to another state or country for work related reasons and are leaving one or more children with friends or relatives for school purposes. In order to do so, we need them to have a court order granting the foster family temporary guardianship. The guardianship can be for a school term, for a school year, for a calendar year or some other limited term, but it's necessary to make the addition.
Depending on whether you stay with the same company or move to a new one, your health insurance may or may not continue to cover your son in Iowa. If it does, fine. If it does not, you have several options. You can get COBRA for just your son. You can buy an individual policy. Or, you can look into the temporary guardianship of the friends or relatives he will be staying with. The advantage to the guardianship is that it also would likely take care of the agreement Quincy mentioned that allows them to act for you in an emergency, but it is not your only option.
Just something to consider as you move forward.