I remember once reading an article that claimed that the best
predictor of success for a child growing up was the social background
in which they grew up: rich/upper class kids did better than
poor/lower class kids out of all proportion to other factors such as
health, intelligence, etc..

I would like to see a study or article that backs this up. I'm fairly
certain the original was on news.bbc.co.uk, but any similar or
supporting article or study will do.

I have already found studies that link success to the educational
achievement of parents: while education is a good predictor of family
wealth, I want a study that links them more directly.