I think questions like this really just boil down to your temperament / philosophy as a parent, and your child's personality. I have a 7th-grader who I'm considering finally introducing payment for grades, because he's motivated to earn money, he's too young to work an entry-level job, and there's only so many chores he can do for his grandparents in exchange for cash (as per their arrangement).

Our time and effort is valuable, and should be rewarded! (parallels to adulthood)

Personal motivation is important to recognize and cultivate! (parallels to adulthood)

As for the idea that payment for grades is a perversion of the sanctity of study, I have somewhat heterodox views on the value of education in the first place; the schoolwork itself is rarely important, but doing the work is. Showing up, participating in earnest, and completing your assignments is important, however pointless the assignment is. (parallels to adulthood)

The actual letter grades don't matter to me as a parent, as either the content being taught is often arbitrary (or dictated from on high by bureaucrats making decisions based on a variety of irrelevant reasons, such as 'the district bought this software/coursework for the year' or 'it's in vogue to teach this in this way now' or 'that's the way it's always been'), or other circumstances may impact the tabulation of the grade (one class may assign a long list of tasks, graded 0-100 points out of maybe 2500 for the quarter, another class may assign half a dozen total tasks, graded 0-10 out of maybe 75 for the quarter ... the latter removing any ability to miss more than a point or two before your grade starts to swan dive, despite actually understanding the material)

IMO, learning should be a life-long pursuit, and learning to love learning for the sake of knowledge itself is paramount. Outside of attending college/university for specific reasons (desiring to be in academia, or studying medicine, law, mathematics, civil engineering, chemistry, or a scant few other subjects that require accreditation to enter the field), I don't have any expectations for him to attend or not attend. It should be a calculated, self-beneficial decision to go in the first place, and for many people who choose to go, it may be more advantageous to do it at 25 or 30 instead of immediately after high school. He'll figure it out. I'm supportive either way and here to guide when the time comes.

Besides, a 9th-grade A+ is a fleeting and ultimately irrelevant achievement; I say teach the kids work ethic, how to learn, how to think, how to recognize the constraints of a system, how to exist inside that system, and how to break the fuck right out of it if/when they so choose.

Ultimately, I encourage him to dive deep into whatever sets his brain ablaze, to not be afraid to fail over and over again as he builds skills and meets people, to be curious and diligent, and to enthusiastically pursue personal satisfaction and fulfillment over fearfully pursuing material externalities as dictated by society at large. A confident, competent person will be equipped to trade their time, knowledge and efforts for cold hard cash out in the real world, so why not just face reality and reinforce that with his current "job" (school)?

That said, if my kid had a different personality, I'd probably take a wildly different approach to all this stuff LOL so please don't take my advice at face value or assume that I'm even remotely close to being right about any of this stuff!!