You're thinking of the children as objects and not people.

Grades and school projects mean a lot to my kids and one of the most important things I'm trying to teach them right now is to have a sense of responsibility and respect for their own work and commitments.

Fair enough, nothing wrong with prioritizing it for the sake of the kid - not for the sake of the school.

Grades might not mean anything, but the knowledge is foundational and really starts to build from middle school onward.

I skipped an entire year of middle school (8th grade), spent a few weeks studying a bit, and it was fine.

Your singular data point may not generalize to all children and all educational settings.

Grades often determine placement for classes in HS. If you want to be in advanced math or honors English, you need good grades in middle school.