Maybe I have bit too positive outlook on this, yeah.

But that article also emphasizes a lot (first half) that a child's environment simply matters a lot. Esp. having parents that have higher education themselves and are there for the child to support it regarding learning outside of school can make a big difference. And this isn't just about the first couple years before elementary school (what article says re "Wortschatz"). Esp. the ongoing school period thereafter. E.g. "Does it make a difference in a child's household if parents can speak English when trying to learn English?" - of course it does!

The point on "Brennpunktschulen" is also very environment driven. I'm not saying that "Lehrermangel" isn't real, or that having this system of three school paths starting from 5th grade is the best invention ever.

But one can't put all the blame on the school system, when "what happens outside of school" has such a big impact on a child.