I didn't even know this was an issue. By 2010 most top schools will require a cashier's check/money order.
The question of whether the school received it or not is iffy. You can't unsend mail, that's for sure. You signed a contract acknowledging the fact that you are sending a $500 deposit in exchange for a spot in the class and placed it in the hands of a courier (USPS). In many states, this is binding unto itself. This is why unlawful detainers are both taped to your door AND mailed via USPS in order to be binding.
I suppose you could argue that subpoenas are not in effect until the time of service, but this is not a subpoena, this is cash in exchange for a service, which is more like a rental contract in my previous example.
By revoking the check, you're technically in breech, even if you decide on day 2 to decline the school's offer. Retail stores charge $25 for returned checks and schools can also pursue legal action in small claims court for issuing a stop payment on a check.
Just remember...oral stop payment requests last only 14 days while written stop payment requests last 6 months. If the school really wants to, they can simply wait for your stop payment to expire and then cash the check. At that point, you have no further recourse. My guess is most schools won't do this, but if they are crunched for money, they just might.
UCC law:
Section § 3-302 of the Uniform Commercial Code defines a holder in due course as
theholder of an instrument if: (1) the instrument when issued or negotiated to the holder doesnot bear such apparent evidence of forgery or alteration or is not otherwise so irregular orincomplete as to call into question its authenticity; and (2) t
he holder took the instrument (i)for value, (ii) in good faith, (iii) without notice that the instrument
has been dishonored,(iv) without notice that the instrument contains an unauthorized signature or has beenaltered
The UCC allows a holder in due course full transferability of rights to assure theholder a free market for the instrument (§ 3-203). A holder in due course has three yearsfrom the date a check was dishonored or ten years from the date the check was issued,whichever period expires first, to sue the maker for recoupment (§ 3-118)
So yes...to answer the question, this is NOT considered check fraud if you have notified the school that you are dishonoring the check. However, the issue with the contract is that you have agreed to pay the $500, and courts have tended to be strict with contractual issues. Are you going to be sued for $500? No, probably not. So this is definitely unethical behavior...somewhat legal and a very low risk of litigation, but still something you should avoid.
But most of you won't care...you got your $500/$1000 back, and that's all that matters to you.