The environment? Yep.
But one compelling thesis stands out, as bizarre as it may appear. It has to do with lead. Kevin Drum has been harping on this point for a while now, and the evidence is very compelling. The Washington Post had a great story on the connection between violent crime and lead levels in 2007:There are so many factors that contribute to the highly complex human activity of learning; this is but one of many. And, like most of them, it is entirely out of the control of a teacher.
The theory offered by the economist, Rick Nevin, is that lead poisoning accounts for much of the variation in violent crime in the United States. It offers a unifying new neurochemical theory for fluctuations in the crime rate, and it is based on studies linking children's exposure to lead with violent behavior later in their lives.
What makes Nevin's work persuasive is that he has shown an identical, decades-long association between lead poisoning and crime rates in nine countries.
"It is stunning how strong the association is," Nevin said in an interview. "Sixty-five to ninety percent or more of the substantial variation in violent crime in all these countries was explained by lead."
Through much of the 20th century, lead in U.S. paint and gasoline fumes poisoned toddlers as they put contaminated hands in their mouths. The consequences on crime, Nevin found, occurred when poisoning victims became adolescents. Nevin does not say that lead is the only factor behind crime, but he says it is the biggest factor.
Is that an excuse to accept mediocre teachers? Of course not. But it ought to shut up those who continue to harp on "bad" teachers as the primary cause of our society's ills. There's far more at work in our world than teachers unions.