I teach in a public middle school. Every class that I teach has quite a range of abilities. At my grade level, the reading teacher has one class for students who need extra support in learning to decode words, and the math teacher has one math class that is allegedly accelerated.
We feel the effects of those classes in the "heterogenous" classes the rest of us teach. We slog through the classes we have in the same time slot as accelerated math (even though kids who are good at math are not necessarily good at social studies), and we breeze through the classes in the same slot as intervention reading.
A couple of years ago, I was teaching reading. I just happened to have a class full of kids who tested at Proficient and Exceeds in reading, with no kids at Approaching, and one kid at Well Below. I worried that it was going to be a lonely year for that kid. In fact, with everybody else on task around him, he stayed on task, and he performed just fine.
The effect that we see in classrooms when we take the advanced learners out, of course, is just a continuation of what happens in public schools when parents who are motivated by academic achievement--and can afford it--pull their children out of the public schools and put them in private schools.
