I've never seen proof of this, nor why it's any different for wealthy school districts where cost-per-student is nominally lower (parental investment notwithsta

I've never seen proof of this, nor why it's any different for wealthy school districts where cost-per-student is nominally lower (parental investment notwithstanding). But that's beside the point, because the notion is always brought up as a way to say that the students themselves are a lost cause.