Feon wrote...
Better grades = better gift
Don't ever do this. I had this classmate back in elementary and this sorta system really fucked him up... just don't do it.
For this bad kid... get him all the gifts he wants but (if he still believes in Santa Claus), fake a letter where Santa says he's watching, and comes with his gifts only after he sees that said child was behaving well. And that this observation might take a loooooot of time.
If he doesn't believe in Santa, just tell him that he gets gifts only when he starts to behave.