I think one of the problems is for kids who are high ability but not high achieving and therefore not likely to be placed in the higher track class. Another concern is for children who would maybe increase in their achievement but are stuck in a certain track without the possibility of moving tracks without substantial effort (this, I would think, would be of particular concern to 2E kids). And I think another concern is for lower-ability kids who come out of less-than-academically-rich home environments that would most likely be placed in lower-track classes, which may have the effect of limiting their advancement in school. So, the issue is fraught with all kinds of concerns. I'm not saying I'm for or against it. I would personally love the option of a full-time gifted classroom for two of my kids, but on the other hand I have a son with attention issues that we're working on improving and the looming math tracking in middle and high school is making us nervous that he'll be locked into a track now when our efforts to focus his attention will likely make him a much better student down the road.
Ability grouping I'm all for and has worked out well our our DC's school. The groups are reassembled several times a year in math and spelling and reading and kids do move among groups as appropriate and there are separate groups for each subject.
