Heres my 2p :)
I agree kids shouldn't need to be bribed and want to do well for their own good regarding exams, but I also realise:
A) Its not an ideal world, and with some kids it can give them a kick up the bum if they are more money focused than achievement orientated & is pretty much the last resort. (My brothers friends mum was at her wits end and came up with the following system:
£50 for an A*
£30 for an A
£20 for an B
£10 for a C
-£5 for a D
-£10 for a E
-£20 for an F
-£30 for a G
-£50 for a U
So, if he got 10 A*s he would of 'earnt' £500, or if he got 10 U's he owed his mum £500.
My mum was seriously considering this with my brother, and tbh it probably would of worked because he is incredible with real work earning money- fab work ethic, but always got crap reports for academic stuff, and I suppose this method bridges the gap.
B) Some kids I suspect are still wayyy too young to understand the long term effects of revising, and short term rewards work better.
C) I wouldn't be against getting the kid a Wii or something if they had worked really hard + you can afford it after the results but not telling them before- At GCSE I got The Sims 3 (I think) & A-level Wii fit and really appreciated it (plus, I think my mum wanted it anyway :P)
:) Just my 2p