For the record, tracking was done in the 70's and the main reason it was considered evil was because a kid was assigned a track and it never changed. So if you had a bad day and ended up in the low track, but were really smart, too bad, so sad.
In true ability grouping the kids are supposed to be periodically assessed(at least once per year) and move groups accordingly.
And by the way, all schools age track. The kids are assigned a grade track when they enter K according to their age. No Child can be Left Behind and No Child may Leap Beyond.
Thanks go out to whoever first posted No child leaps beyond. My faulty memory cannot recall who the credit goes to.
