Yes this is true. But it doesn't seem that big to me: 10% extra budget isn't nothing, but it's at a few schools which are competing with private schools, which

Yes this is true. But it doesn't seem that big to me: 10% extra budget isn't nothing, but it's at a few schools which are competing with private schools, which (I think) charge more like 2-3 times as much. And this is the top fraction of 1% of public schools. The merely top-20% schools, nice suburbs far away from wall street, they raise a fraction of this. I don't think it can explain very much of what's different there compared to the bottom-20% schools across town.