I will try to make this non partisan, but there is sadly a strong correlation in these links.
The issue isn't so much total levels of funding. It's even levels of funding, with many schools being underfunded especially in rural and minority districts
First, TCF isn't non-partisan; it's a progressive institution.
More importantly, TCF's "underfunding" metrics assume the conclusion of the debate you're having here. They're generated via correlation of expenditure to 3rd and 5th grade reading and math scores. But if your argument is that increased school funding is an inefficient or even ineffective way to increase 3rd and 5th grade reading and math scores (or, more subtly, if you think those narrow measures aren't durable through 12th grade) then the TCF study isn't really a rebuttal to that argument at all, is it?
Relative to what? The US spends among the most of any country on education. https://www.mercatus.org/sites/default/files/International-E...
If the assertion is that education is underfunded everywhere in the world, that’s an interesting assertion, but what’s the basis?