They did that at my school too - though not for English. It was a total crock. The underlying reason seemed more to keep the troublemakers and overtly "dumb" kids away from the others, rather than to seriously accelerate learning. In the UK, there's a fixed "National Curriculum" and so there's no point in them teaching above it (or even off of it - we entirely skipped set theory, for instance, as it wasn't on the NC for that year).
What was the most difficult mathematics class at your high school? At what grade level did its students take that class? How many students were enrolled in that class?
I'm not the parent commenter, but where I went we had up through multi-variable calc and linear algebra, though really I thought the toughest was Prob/Stat in HS but that's probably because the teacher wasn't very good at motivating students. P/S was required on the 'accelerated' track- the accelerated track prepped you to take the BC Calc AP exam which will test you out of Calc and Calc 2. The Multivariable and Linear classes were both elective credits and only half a year each, and also there were no AP tests so you had to convince your college to let you test out of them on your own (though I can't imagine anyone had any problems with that). Both those courses had maybe a dozen kids in them (in a class of 400ish), and it was taught by the same teacher we had for Calc and Pre-Calc our Junior year.
Truly the best teacher I ever had without any doubt, had a passion for the math, the students, the teaching, and did an amazing job motivating a few of us that were used to doing the bare minimum and gaming the system (which as has been noted is what ends up happening to a lot of 'gifted' students). If only all our teachers (or hell, most) had half (or a quarter) the passion she had, our schools probably wouldn't be failing like they are. Not to take anything away from the great teachers out there, they exist, but the system just drives away the best ones.
