Well if anyone is interested, HM was superb. Told him I wasn't a fan of saturday school, school week was long enough (too long), weekend should be family time, couldn't see the benefit to the child etc etc, didn't object to matches but if he couldn't fit in everything in the week then why couldn't he lop time off our very long hols or lose some extra curricular stuff. but the long and the short of it was I couldn't see myself bringing dd to sat school.
he was not at all defensive, thought I had some great ideas, was surprised to hear that lots of parents loathed the idea of sat school (thought they were just ambivalent), agreed that school hours were too long, said they were just looking at the curriculum to try and finish everyone during the week at 4.15 and do only optional extras and optional prep afterwards, would now also look closely at sat school and how it should change.
thinks having an optional programme every other sat mornings (eg cricket nets, some music, etc) with fixtures in the afternoon might work well, which I'd be completely happy with. he knew about sherborne prep (we have a governor in common) and said he was going to speak to them and a few other schools who had scrapped sat school to see how they had rejigged it - basically the whole conversation couldn't have gone better.
spoke for about an hour.
I am so impressed. And reasonably confident that things will change. And he also told me that even if things didn't change immediately (as it would require a fundamental alteration in the whole timetable) that if I felt strongly about it dd needn't go, but he thought I had raised so many interesting issues about the whole timetable that he was quite fired up about changing it
so the moral of the story is - if you don't like it, tell them!
I'm so relieved