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.
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.