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.
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.