Increased funding did improve educational outcomes. It just didn't improve it enough to be considered worthwhile.

The fact is that educational outcomes are caused by a large number of variables. Areas with (historically) poorer schools have less competent (or more corrupt) administrations so money doesn't go as far. Even with good leadership at the top (superintendent or public school committee), if the source of that money is not something you can rely on consistently enough to pay salaries with then you are not going to see significant changes.

Pre-K education is also critical to determining later school performance, as knowing the alphabet and numbers are practically assumed by kindergarten curriculums as they are covered far too far to be more than a review. But we have not tried that yet, so we'll see if that pans out...