My man is a prep/private school boy and although he had a great time during his youth years, I am shocked at the level of education he received. I went to a very average public school and my general knowledge/spelling/grammar/maths skills etc... are certainly superior to his. Fair enough, I was a good student, he wasn't!
He stopped after his 'A' levels, I did a Masters, so in the end, our education in total probably cost about the same, and the result is that we both have pretty good jobs (different sectors) and earn about the same!!
His mum is very keen on my sending my children to private schools too. I don't see the point at all. They currently go to an excellent primary school, i couldn't ask for better education and social environment. My daughter is very advanced, evaluated at 2 years ahead, but she is never bored and is challenged at her level. My boy is doing very well too and the little shy boy he was when he started has now become a confident pupil with many friends. The secondary school they will go to is excellent too according to all the people I know whose kids go there and OFSTED report classes it at very good.
If the local schools were clearly a problem or my kids had special needs that required more individual attention, I would probably consider funding private education, but as it is, they are happy, learning as they should and well, I much prefer spending the money on our family holidays than for them to go to private school!