I think a well written letter from a law firm will persuade them to just refund your money.
(law firms tend to be a little more intimidating)
Unless you signed a specific contract that said the money belongs to the flight school no ifs, ands, or buts, then the school has no legal recourse to keep the funds. Even so i would still get an attorney to send a threatening letter. You'd be surprised how quickly they will take you seriously.