Here's an article K. Cleveringa found on the topic. Quotes from a New Republic article (which is a legit source).
And incredibly, it combines the Expert Performance Movement we talked about in child soccer and the number and type of words addressed to children in differing economic levels.
And, be sure to read the readers' comment section for some good back and forth. I'm not sure I agree with this guy's conclusions about when it all went wrong--and the numbers aren't there to back it up as far as church going is concerned.