One interesting nugget in international student test scores released today by OECD is that the countries with the smartest students also reported the unhappiest kids. Korea, for example, boasts the best math scores in the world, but also has the least-happy students. Indonesia's kids report being the world's happiest students, but they produce the world's second-lowest math scores. Click the chart to enlarge (to be clear: this is self-reported happiness in school):

Is there be a relationship between math and misery? Economist Justin Wolfers runs the math. The variation is pretty large (Eastern Europe seems egregiously unhappy, while southeastern Asian students seem to be having a unduly good time in class), but the correlation is statistically significant.

There are so many ingredients here—culture, economics, happiness-based expectations—and I'm not going to pretend I can explain why several million children are happy or unhappy in their classrooms. (Students in the United States fall below the OECD happiness average, too, by the way.) But a simple hypothesis would be that kids in Korean and Finnish schools, who have notably long school hours, are, after all, just kids. And it's not a revelation that kids don't like working too hard.