(CBS) — The parents of 17 students at Hinsdale Central and Hinsdale South High Schools have been sent some big tuition bills.

District 86 began checking the residency of all students at the two schools last year. Spokesperson Karen Warner says letters were sent to the students’ parents about six weeks ago demanding proof of residency or payment.

“Hinsdale residents are all taxpayers if you are renting or owning and you are paying that cost,” said Warner. “They pay significant property taxes that support the schools. In order to have them realize the value of what they are paying, they need to be sure that they are getting what they are paying for.”

Divorce is a common reason for attending out-of-district. Tuition is more than $16,000 dollars a child. There is an appeals process.