Tragedy of the commons - enough parents don't see their kids as anything but perfect to dissuade teachers from wanting to talk to the parents about issues their little darlings have.

That said,

> Common core math makes it impossible for parents who did not learn common core style calculation

Is false. I didn't learn common core as a child, but I was able to pick it up as an adult. There's a lot of good resources online.

Tip: It's how most of 'us' do mental math, spelled out and codified. Rough estimates refined in further steps.