DS is as at state primary (Ofsted 'Satisfactory'). I am a doctor and we could afford prep school fees, but I prefer state at pre-prep/ prep level. I was privately educated throughout. DS loves his school, but will be sitting entrance papers for private prep shortly, as I am not certain he would get in if we left it later (he is 8). Already at state school they are working approx 1 year behind the local private preps as standard.
For me state primary meant local friends, diverse social mix, no long journeys to & from school, no Saturday school and better school/ life balance. But this has to be balanced with enormous classes (his class has 34 children in it), relatively poor discipline, the constraints of the national curriculum, rubbish sports provision etc. We supplement his learning with quite a lot of work at home, and I have become as involved with the school as possible (I'm a governor, for example).
DD (4) will start state primary in September, and I will aim to move her to indie at around 8/9 also. But she seems to be quite a lot brighter than DS, so may move a little later.
My colleagues are divided on this; approx 50% send their children private, but more move to private at secondary level. Contrary to popular belief we do not all earn mega-bucks and we do all work very long hours; we are therefore at the income level where we could do it, but not without batting an eyelid, so it is attainable with sacrifices, IYSWIM.