Educational funding has a self-reinforcing element to it driven by failure. Succeeding schools do not get funding increases while failing schools tend to get more resources. Since schools fail or succeed not by funding, but by other factors, failing schools get into a funding loop. Failure leads to more funding, but funding doesn't matter thus continued failure and more funding. Hence why failing districts are also the most expensive. Cheaper school districts are cheap because they're already doing well.
And this is why I'm opposed to the entire concept of public school. Government doesn't understand anything beyond spending more money to try and solve problems.