Hello ...
We do not pay for grades, but we do offer rewards for efforts if we are trying to instill certain behaviors or for efforts toward improvement. We also "celebrate" good report cards ...usually w/ dinner out or ice cream.
While we do not pay for grades, our family does have an example of how paying for grades ONE time was instrumental in turning things around. My husband struggled in grade school and was labeled as academically challenged. My m-i-l disagreed and thought he was bright based on what she experieced at home. She routinely would be in the school on his behalf only to have the teachers/admin/system blow her off and basically say, "sorry, your child's just not that bright." However, several things came into play to finally prove 1) yes, we're right ... he's bright and 2) obviously this kid needs motivation. First, of course, they took care of the hearing & vision things. Then, they noticed ... here's a kid who is nearly failing everything and the school has labeled him as below average ... but he gets a 100% every time on his spelling. Why? Because the kids who got 100% got a sucker. In 5th grade, my husband's teacher rewarded the kids who read the "Lord of the Rings" trilogy by carving their name on a big walking stick. My husband wanted his name on that stick ... so he read the books even though they were way beyond his reading level at the time. That teacher ENCOURAGED him when the others didn't ... and it instilled a love of books that made all the difference in the world.
Finally, not long after that time ... my husband's dear father offered to pay $20 for every A on my husband's next report card. Since this was a child who had mostly earned C's and D's, my f-i-l made it extreme because he thought he could ... he never dreamed he'd pay out anything at all.
You can imagine his surprise when my husband brought home ALL A's the next time.
Good to his word ... my f-i-l DID pay. But he also made a point ... said, see, we know you can do it now and we expect this effort from now on without the money. And, that's pretty much what they got.
My husband went on to graduate 2nd in his class and scored either a 34 or 35 on his ACT.... not bad for a kid the system wanted to continually label as borderline "academically challenged."
I wouldn't pay for grades on a routine basis, but I DO believe there might be times when it could work.