> teach all students at the level that would have been taught only to gifted students before?
You just can't do that, no matter how much you want it. Some teachers are better than others, they can't all be elite. The teachers union wouldn't let you sack all the mediocre teachers, and even if you somehow could fire them, where would all the new elite teachers to replace the mediocre ones come from? If you just sacked the bottom 50% of teachers and doubled the class size of the better half, I think classroom conditions would certainly deteriorate.
You just can't do that, no matter how much you want it. Some teachers are better than others, they can't all be elite. The teachers union wouldn't let you sack all the mediocre teachers, and even if you somehow could fire them, where would all the new elite teachers to replace the mediocre ones come from? If you just sacked the bottom 50% of teachers and doubled the class size of the better half, I think classroom conditions would certainly deteriorate.