Our experience (in Menlo) has been that almost all of the teacher's small-group or 1-on-1 time is spent with kids who are behind. It is understandable to have a goal that is bringing up the lowest performers. But if a school is going to do that, they should not steadfastly refuse to let kids be tracked.
Allowing tracking would let kids who are not behind actually grow to their capacity. As it is currently structured, the kids at the top are never challenged, and they may not even realize that so many of their peers are also talented and unchallenged.
Teachers shouldn't have to teach a span of 3-4 grade levels. But in our district, the teachers and administration are the ones who are fighting hardest against tracking. It's not fair of them to fight tracking and then complain that teaching advanced kids would be too hard. It's only hard in the current system, where tracking (in our district) is not allowed.