I think it’s become tragically obvious that a whole lot of children are born to parents who should’ve never had children and have no business being parents. These children end up dumped on educators with zero support at home, and so little social system support we could also say it’s zero.
This isn’t nature versus nurture per se (although I believe the data does show some ability and intelligence is genetic/inherent), but that it takes a lot for a human child to succeed unless they’re at the higher end of the bell curve (and even then it’s no guarantee).