Statistically speaking, tracking tended to diminish learning and boost inequality wherever it was tried. In general, the younger tracking happened, the worse the entire country did on PISA. There seemed to be some kind of ghetto effect: once kids were labeled and segregated into the lower track, their learning slowed down.

PISA was developed by a kind of think tank for the developed world, called the Organization for Economic Co-operation and Development, and the scientist at the center of the experiment was Andreas Schleicher.

This strange new test called PISA, which stood for the Program for International Student Assessment. Instead of a typical test question, which might ask which combination of coins you needed to buy something, PISA asked you to design your own coins, right there in the test booklet.

Economists had found an almost one-to-one match between PISA scores and a nation's long term economic growth. Many other things influenced economic growth, of course, but the ability of a workforce to learn, think and adapt was the ultimate stimulus package...For students, PISA scores were a better predictor of who would go to college than report cards...PISA wasn't measuring memorization; it was measuring aspiration.