if his situation is anything like mine was, then the answer is likely to maintain good grades to support future educational prospects.
which is unfortunate as this system encourages the pursuit of the grade over the pursuit of knowledge. it took me many years to shake that mindset.
(Indeed, one reason homework may be harmful is the way it can create an adversarial relationship with teachers and condition students to ignore teacher suggestions and feedback).
You have to excel in all coursework on the default track to competing in race of society. There are opt-outs/alternatives popping up, but they're not mainstream.
There are two cultures in the US.