@DrewDad,
That's so dangerous, though. Tracking was big when I was in grad school for education, just starting to fall out of favor, because of lots of recent studies that we looked at in classes. There was a lot of scary stuff about kids being stuck in their tracks -- that is, if they were put in a "lower performing" group in kindergarten or first grade, they stayed in it throughout their education. Whereas if there was more interaction between various skill levels, that didn't happen to the same degree -- a lot more kids' performance improved.
What was especially scary about that was that there was a high correlation between socio-economic background and where the younger kids were placed in tracks -- that is, a lot of times it was the poor kids who were put in the "lower performing" tracks and stayed there throughout. Whereas they'd often do quite well in other circumstances.
Then there are also, counter-intuitively, gains for higher-functioning kids when they are in a position to help their lower-functioning peers. Knowledge is reinforced, and other good stuff happens. (My kid, who's been ID'ed as gifted and gets special services for that, loves helping other kids and I think gets a lot of benefits from it.)
The whole education problem is a big one, I've become convinced that the single biggest variable is simply the quality of the teachers. (This has been my view for the past 15-20 years and I'm seeing more and more studies about it.) It's a really hard variable to control for, though.