Hi hatwoman
Yes, this has been pretty much the story of my dd1, and it kicked off properly in Y2, although we had rumblings earlier.
I think it all depends on the attitude of the school as a whole and of the individual teacher. Your post of 4.32 is entirely sensible; however, although it may seem bleedin' obvious to us it doesn't to the school, ime. Some schools deal with this kind of thing well, and have sensible workable strategies in place to keep the fast learner engaged. Others don't.
From our experience, dd1's happiness levels have varied powerfully from year to year, although the primary curriculum has never really met her needs, if we're honest. It's been manageably okay in years where she's had confident experienced teachers who like her as an individual, and can take it on the chin when their mistakes are pointed out and can cope with being asked questions they don't know the answer to. In years where she hasn't (Y2 and Y5 spring memorably to mind) it's been all-out war, dd1 being sent out of the classroom, sent to heads office, letters home etc. And not for major league disruptive behaviour, but just for talking, for reading her own books under the desk, and for arguing/talking back to the teachers.
I nearly moved her (yes, I confess it, to a private school) for Y3. In the end I bottled out for a range of practical, financial and emotional reasons, but with hindsight it was a mistake. She's an exceptionally focussed child and has, I think achieved the same level academically as she would have done in the private school, by dint of extra work at home, odd bits of tutoring, and us simply making resources available to her. But she hasn't really enjoyed school, and has intermittently become quite lippy, cynical and disaffected, and generally difficult to live with.
In your situation I would do the following: have a word (as non-confrontationally as you can) with the teacher, to get a feel for the lie of the land. If you don't like what you hear, make an appt to discuss with the head, and see if you like that any better. At this stage in the year you might as well wait to see how next year kicks off, then repeat as above. If nothing changes you probably need to accept that that's how it will be, with minor variations according to individual teachers, and develop strategies either to live with it or to move school. FWIW I think the structure of the National Curriculum and SATS focus makes it very difficult for all but the most exceptional state primary schools to cater properly for naturally very academic children within the mainstream classroom.
hth