Mississippi State Senator Willie Simmons, who at the time represented Sunflower among other counties in the Delta, said that the state of Mississippi once used elementary school achievement scores to project future prison population. Simmons worked in corrections for 17 years and in 1992 was the deputy commissioner of Mississippi’s Department of Corrections. In that job, he said, he commissioned a study to project what the state’s prison population, then about 10,000, would be in 10 years.

Don't want to go necro on you :) But since you've had a recent comment:
http://www.nytimes.com/2009/04/16/opinion/16krist...

interesting Op-Ed on IQ. Not exactly the same, but I think the causation is similar: children who are given more chances to read/learn become smarter and read/learn more. Obviously, this requires schools to step it up, but I think the majority of the obligation lays with the family. The family issue also compounds on the link between reading and prison construction: not only is not being able to read well harmful in and of itself, but it also signals what is going on with the child's environment.

I don't know how interested you still are in the topic… I obviously have access to a lot of research from the economic perspective that I could go through in my free time. Peace!