My high school was one funded by the Bill and Melinda Gates foundation and we tried to limit tracking as much as possible. For the first two years, there is absolutely no tracking. The idea is that the faster learners will help their slower peers who benefit from more interaction with their friends. Anecdotally, it seemed to work rather well but required students to initially be motivated to learn. My school never really had a problem with that because students applied to the school and could opt out of the application process without their parents knowing.
Anecdotally, I was always annoyed when I was dumped into a class with the slow kids and had to help them catch up while I was bored out of my mind. The 'no child left behind' mentality has slowed a lot of kids down instead of letting them learn enough to keep them interested in the material.
