A growing body of literature now suggests that the earlier we turn back the clock in kids’ development, the more profound the impact of their environment. Early childhood is critical—race and class differences in achievement are pretty much evident by the time kids reach kindergarten, for instance. Even what happens before you’re born turns out to have consequences for decades afterward. The Chernobyl nuclear disaster lowered the IQs and graduation rates of kids who were in utero all the way over in Sweden, where some of the radioactive iodine blew. An earthquake in Chile resulted in fewer boys being born (boys are a riskier genetic bet and thus have a higher rate of miscarriage under stress) and lower achievement among those whose mothers were closest to the epicenter. If pregnant women fast during Ramadan, their babies suffer. And so on.