In most places in the US, the amount paid to schools has gone up far faster than inflation over the past several decades, while the schools have produced no significant improvement in educational proficiency with the extra funding. It changes somewhat with exchange rates from year to year, but it is often the case that every country that outperforms the US in public education spends less per student than does the US.

So, if giving the schools a lot more money bought no better educational results, then continuing year after year to increase funding beyond inflation, spending more than any educationally superior country, still left educational outcomes essentially unchanged, what are the chances that the major problem is the level of funding?

Isn't it a lot more likely that the major problem is what the school systems actually do? If they could show that each 10% increase in funding in a given location had produced an average 40 point gain in SAT scores, I would want to talk about further funding increases in that location. On the other hand, if they showed that each 10% increase in funding produced, well, 10% more for the staff but nothing for the students, I would want to discuss changes other than funding.