I think the idea of paying for grades is built upon a false premise: that grades matter.
Lots of kids get good grades but don’t really learn. They just know how to game the system of tests. While that may get them into a “good” college, it is meaningless in the long term.
In the long term, what matters – and it can’t really be taught or coerced into a child – are two things: (1) the fundamental intellectual curiosity of the person (intellectually curious people figure out ways to learn about things – inside or outside of school), and (2) inner discipline (that is, a willingness to bear down and work, even when you’d rather not). If you’re not curious about the world and/or are unwilling to put in the work… your grades will get you nowhere.
My brother was a poor student in high school. He was very intellectually curious – read like a madman – but had no discipline for school. He ended up deciding on his own that he needed discipline and went to a military college where he did very well. Then on to a prominent law school and now he’s a federal prosecutor. My point is that his grades up until the time he graduated from high school sucked ass. But it all turned out pretty well in the end because he eventually figured out on his own that he needed to develop discipline.
In my opinion, focusing on grades is placing too much focus on the trees, as opposed to the forest.