Many of the public policy disputes over education, whether at the K-12 level or at the higher education level, quickly turn into disputes over how much to spent, or whether "enough" is being spent. For some international perspective on these issues, the Condition of Education 2018 has just been published by the National Center for Education Statistics (May 2018). It's chock-full of useful tables and figures, but here are a few from the "International Comparisons" part of the volume.
First, look at spending per student in OECD countries, as compared with per capita GDP. As the figure shows, the relationship is pretty much a straight line, in which countries with higher per capita GDP spend more on K-12 education. This makes some intuitive sense, given that teachers are one of the main expenses in any K-12 system, and when a country has higher capita GDP, wages in general and pay for teachers in particular will be higher, too. The figure shows that while a few countries spend a little less than one might expect on K-12 education based on their per capita GDP (Mexico, Ireland) and some spend a little more (Korea, United Kingdom), most countries are quite close to the predicted line, like the United States.
Of course, this doesn't prove whether the US should dramatically change its level of K-12 education spending. But it suggests that US K-12 spending is not out-of-line with the rest of the world in this area.
What does a similar figure look like for higher education spending? Some interesting patterns emerge. For example, Mexico spent less on K-12 than one would predict from per capita GDP, but spends more on higher education. Conversely, Korea spent more on K-12 than one would predict based on per capita GDP, but spends less on higher ed. The United States spend way more than any other country on higher education on a per capita basis, and way more than would be predicted based on per capita GDP.
Of course, this doesn't prove whether the US should dramatically change its level of higher education spending, or how US higher education is delivered. But it suggests that the US higher education experience is different from most of the rest of the world.
Here's one more comparison, looking at the share of adults who have a postsecondary degree of some kind. In the figure, the light blue bars show the share in the 55-64 age bracket who have such a degree, while the dark blue bars show the share in the 25-34 age bracket with such a degree. One would generally expect that as higher education expands, a larger share of those in the younger group should have postsecondary degrees, compared with those in the older group, and this pattern holds for most countries.
But notice that for the US, the age 55-64 group was in general more educated than the rest of the world, with the exception of Canada. But for the 25-34 group, the US is still above the OECD average in share with a postsecondary degree, but a number of other countries are now substantially ahead, and the US is much more middle-of-the-pack. When combined with the previous figure, this makes some sense. Given that the US spends vastly more on a per person basis for higher education, it's more costly for the US to provide a big expansion of higher education for the young adults of today.