Class sizes in private schools are a little less than half of what they are in public schools on average. That includes "private" schools (like a catholic school).
As a parent now, I must say I don't understand what you want parents to do. I want the best for my 3 daughters ... and public school isn't the best (and private school, while far from free, is certainly not as expensive as I keep reading. Tuition per year is in the thousands (close to 10000$), but not 50000. And if I chose the catholic school, which btw is a school with actually a better reputation than their current private school, it would be less than 2000$ (plus a third kid doesn't pay at all). One kid has a sponsorship in the private school, and doesn't pay.
When we went to check out the public school, the teacher didn't know where France was, and the 6th year math teacher didn't know what differentiation was. There were no advanced classes or study sessions outside of regular hours (they might refer you to a program that was organized by the state university ... a 45 minute drive away). There were some sport clubs, but nothing compared to either the private school or the catholic school we checked out (there the private school was far superior, you can even go horseback riding, but the catholic school still had 10 sports available, and another 10 activities)
It's close to 2000$ per month to have 3 kids in private school ... and me and my wife pay that because, well, in my opinion there's no alternative.