How can I avoid having to pay back reimbursed tuition to my school district, if I resign at the end of my contract?What can the district ultimately do if I do not pay back the money?
This question cannot be answered definitively without a review of the actual contract. Does the language of the contract provide that you must reimburse the school district whether or not the contract is renewed? If it does, then I see no way out of having to repay the tuition costs. I would advise you to have an attorney review the contract for you. Sometimes local bar associations make attorneys available for a reduced cost for one initial consultation. If the terms of the contract are written as I suspect they are, you can certainly be sued by the school district.
As a practical matter, it is probably inadvisable to skip out on your obligation. Whether the school district sues you or not, it is unlikely to provide you with a favorable reference, and even if you do not rely on this employer for a reference, bear in mind that people in school districts exchange information routinely, and you are likely to be placed on a "Bad Hire" list in your area.
As an ethical matter, do you really want to avoid your obligation? It is ultimately the taxpayers whom you are cheating, and if teachers did this routinely, there would be terrible consequences for teachers, students, and taxpayers.