countess I have worked at comps where that attitude is most definitely prevalent.
Certainly not because the teachers don't care, or are no good at their job. But, because they are under enormous pressure to make sure pupils get those C grades.
They do not have the luxury, or time, to 'focus' their attentions on already gifted students. I mean, yeah...we'll put them in a top set, but really they can virtually teach themselves.
I know this, I have seen it in action in the comps I have worked in. I am an English graduate, with post grad studies under my belt and a qualification that allows me to teach in a FE college.
But, when I was working as a TA in comps, in English lessons, both me and the teacher were focused on the kids who were struggling. I never got to work with the more gifted kids, where maybe I could have given some useful input, beyond the basic lesson content. And, the teacher only usually gave them slightly differentiated work, and they were left to get on with it.