The two previous post are absolutely correct but I should also add that in paying as you go - the control rests in your hands, not the flight schools. So if you aren't happy and decide to fly somewhere else, a lenghty wait for a "possible" refund isn't an issue. Reputable schools won't insist on pre-pay unless you're hour building and looking for big discounts. I can't understand why people are so willing to hand over tens of thousands of pounds/dollars upfront but I guess it's the lure of airline 'connections'. No play on the latter word I might add.