I seriously doubt the predictive power of most EC's to predict those things-- those wind up being proxies for SES; and yes, SES has predictive value all by itself. Maybe not because those kids are smarter inherently, but they are almost certainly better prepared.
No, they're definitely smarter.
Being poor reduces your IQ by 13 points due to the cognitive load of obsessing about money problems, such as keeping the heat on and the light bill paid.
Where do poor people go here, my clients ask me.
The woods, I say.
Which is true.
They also ask me what happens when the money runs out.
You become homeless, I say.
Which is also true.
"Poor people spend so much mental energy on the immediate problems of paying bills and cutting costs that they are left with less capacity to deal with other complex but important tasks, including education, training or managing their time, suggests research published on Thursday.
The cognitive deficit of being preoccupied with money problems was equivalent to a loss of 13 IQ points, losing an entire night's sleep or being a chronic alcoholic, according to the study. The authors say this could explain why poorer people are more likely to make mistakes or bad decisions that exacerbate their financial difficulties."
http://www.theguardian.com/science/2013/aug/29/poverty-mental-capacity-complex-tasks
