That's true to an extent, but much less true of Catholic parochial schools. In fact, such schools will sometimes have a population with average income less than the local public schools. Of course most parochial schools won't have special education programs, so that's a huge filter, but as I pointed out doesn't account for the budget gap.

In any event, "picking your customers" is exactly the point of the previous poster(s). Money doesn't really explain what we're seeing. Once upon a time there was a very strong correlation, and people presumed causation, but now it's quite clear that the causation wasn't there. Certainly not directly, which is why throwing more money at the schools isn't helping.

It's doubtful that a catholic parochial school has ever turned away a catholic student. Certainly if that happens, it must be rare. If catholic students are superior to non-catholics, through some self-selection process, how does that invalidate his point? They're not being picky intentionally. A great many admit non-catholic students, often on scholarship, those students also tend to do well.

Public schools have to take children that do not want to be there and make it everyone's problem, and their classmates suffer for it. Maybe this public school policy is the issue that should concern you.