do all schools offer a discount
No.
And those that do should only be offering a discount that works out at about 6% APR. If they're offering a larger discount than that it means that they're trying to borrow money from you for
more than they ought to be able to borrow from the bank ... which means that they've tried borrowing from the bank and been turned down.
Does any student pilot really want to lend money to an organisation that the banks think is too dodgy?