I linked to Dana Goldstein's post on this in yesterday's Fallout, but it's worth addressing again:
In the new education documentary "Waiting for Superman," we hear a lot about how the Finnish education system is the best in the world, but nothing about how much easier it is to be a parent in Finland, because the government provides universal low-cost daycare, nursery school, and health care.
Why don't we talk about parenting more? Because we American optimists want to believe that kids can overcome the deficits they bring from home without having to wait for the United States to become a social democracy (as if). There's also a long and disturbing history of affluent white people judging the parenting skills of everyone else. But I do think there is a limit to how much transformational education reform we can do in the United States without looking seriously at why raising kids is do damn difficult in our winners-take-all society.
I think this is exactly right, although I don't think the fact that external social and economic factors have an incredible influence on how a child ultimately does in school means that teachers shouldn't be expected to meet certain minimum standards of performance in order to keep their jobs.