Lots of people want their kids to get better grades. Lots of people pay for tutors or extra after-school education. You could directly pay your kids to get good grades. This seems strange and possibly bad, though I’m not sure why.

1. I had friends in the early 90s who were paid $20 per A on their report card. This was very foreign to me; getting good grades was considered a baseline expectation in my house (I did not study, do my homework, nor get good grades. I’m about 99% certain that $20 per-class per-quarter would not have motivated me to do any of those things).
2. There is some evidence (but I’m never sure of the quality of evidence in behavioral sciences) that adding an extrinsic motivation to something decreases intrinsic motivation. Thus the fear that paying kids for good grades would decrease their desire to perform well out of some internal sense of pride.