United States schoolchildren are not the highest performing in the world, on average. This is well known and constantly cited in various calls to arms, from the memorable “hostile foreign power” rhetoric of A Nation at Risk to garden-variety speeches warning of economic threats from brainy children in Beijing and Bangalore. The track record is spotty, to be honest — remember when the 240-day Japanese school year was going to lead to total American subservience under the yoke of the Rising Sun by the mid-1990s? There’s also plenty of controversy over tests and methods. But the underlying point seems fairly indisputable — children in some other countries learn more. For example, here’s how things look on the 2007 TIMSS 4th grade math test:

We do okay, indistinguishable from the mean among OECD countries and better than the average of all countries, but substantially worse than Hong Kong, Singapore, Taiwan, Japan, Russia, England and a few others. Eighth grade scores look much the same.

But the tricky thing about looking at average performance in the United States is that our education system is unusually large, diverse, and decentralized. Parts of it are really good. Other parts are shamefully bad. And in a number of important respects, we can only improve the system part by part. So it’s worth knowing just how well those parts are doing. Thankfully, Gary Philipps of the American Institutes of research has done a service by converting state and city-level scores on the NAEP to TIMSS equivalents. Here’s what he found:

Turns out that a few of our states are on par with the world’s highest performing countries when it comes to educational achievement. Massachusetts in particular stands out, and four other states — Minnesota, New Jersey, New Hampshire, and Kansas — received grades of “B,” up there with the likes of Japan. On the flip side, there were a bunch of C’s and one D+ in, of course, Washington, D.C., where fourth-graders learn math at the same level as Ukraine.

This is useful information. International comparisons are often shot down on grounds of fundamental non-comparability. After all, Singapore and Hong Kong are tiny little bits of Asia that just happened to have been sequestered into autonomous political entities by the British because they were advantageously located for international commerce. Countries like Japan and Finland (which tops the PISA test but doesn’t participate in TIMSS) have unusually homogeneous populations and strong cultural ties among citizens as well as other beneficial non-education factors — strong social safety nets, low crime, school-oriented cultures, etc. They’re just not like us, the thinking goes, so it’s unreasonable to compare us to them.

But New Jersey isn’t an autocratic city-state on the tip of the Malay peninsula or a Nordic socialist paradise or anything like that. Nor is Massachusetts (well, maybe the socialist part) or Minnesota or New Hampshire or Kansas. They’re all medium-sized states in America, subject to American laws, filled with lots of Americans in all the diversity that makes this nation great. Massachusetts in particular, the highest-performing state, is full of people from all manner of racial, ethnic, religious, and economic backgrounds. It has relatively high business taxes and relatively good social services compared to other American states but it’s far from France or Finland or Japan.

On one hand, this should make us optimistic. American school systems can in fact compete with the world’s best — some of them measure up very well right now. On the other hand, we should be sobered and far less willing to explain away the inadequacies of our worst-performing states on the grounds of vast, irreconcilable differences of politics and culture.