That's a little better. Granted, it's difficult to quantify things like socially outgoing and confident. Also, that's still not quite what the author is arguing here.
It's not about general social skills or confidence, but about specific (and subconscious) knowledge about how to navigate certain social dynamics that are foreign to some kids and very familiar to others.
"Show me statistics that say rich kids are socially outgoing and more confident than middle class kids."