Those reports are fudged. Here's how the thing works. The per pupil expenses compare a very select group of private schools to public schools. The private schools can "cherry pick" students. That means they don't accept students with severe learning disbilities, emotional problems, etc. etc.
Public schools don't have the same luxury. They have to accept everyone, which means additional facilities and staff that adds to the total.
But what is interesting, the guys doing the studies also cherry pick. They tend to compare public schools to selct private institutions, such as a religious school. They don't compare public schools in poor neighborhoods to those in rich neighborhoods or to elite private schools.
That would change the dynamic. Public schools in Westchester (a suburb of NYC) spend a fortune on kids and get results. The same is true for the elite private schools that run forty to fifty thousand a year.
In the affluent suburbs and among the elite private schools, the system isn't collapsing, it's actually improving.
That's not a huge percentage of the population.