Ever heard of "No Child Left Behind"? The government provided a set of minimum requirements everyone should meet, yet provided no metric gathering beyond the minimum, no funding for advanced studies. Result was a huge decrease in funding for gifted students and there's been several studies on the negative effects.
In my opinion and personal experience, it was awful for any gifted children and all the gifted programs were drastically cut.
One size fits all classes are not the answer. Kids are too varied in aptitude.
You can select for people for are actually interested, and you’re really just introducing the students to concepts that are worth there own class to get to the level where you can actually apply them.