In the schools local to me, there is very little of the "sectioning off" Mag 14 wrote about. The current thinking is to keep everyone mixed together in the classroom. It was better (educationally, if not socially) for nearly all of the children when they were "sectioned off."
As to what Scrap Iron was talking about, (the removal of those who don't want to learn) that is a completely different category than learning disabled and gifted. The learning disabled and the gifted want to learn.
It is totally unfair to those who want to learn when they are roomed together with those whose only goal is classroom disruption.