This keep gifted kids challenged while not pushing anyone through too fast.
There is a difference between subjects as well. I've been in choir with some "intellectually challenged" kids who had great voices: I was the one being challenged.
You're trying to waffle. Have your cake and eat it too.
If you can recognize the fact that there are times when you're just holding back some students, then propping up a gifted student in a normal class to "inspire" the rest is doing a disservice to that gifted student.
We aren't talking about children who are simply "smart", we're talking about children who are so far beyond their peers, it's clearly noticeable. It's the opposite end of the bell curve. Because we're talking about children who are testing at 135 or above.
Let everyone spend some time grouped by ability. Don't just burden them with more busy work. And please make sure the teachers running special programs have a clue what they're doing to kids...
edit: Furthermore, I always thought it pathetic that I went from being a very average student in 2 other countries, moved to America and was suddenly seen as a gifted genius who was years ahead of my peers in math and science. I've obviously never seen it that way - I think kids are capable of for more than the American school system expects of them, but their intellectual growth is being stunted at a very young age.