An article in the Detroit Free Press, "High lead poisoning linked to lower test scores in DPS" by Keith Matheny from 2/25/13, reports on research that matches blood test results for lead in 21,000 Detroit Public School students with those students' elementary and middle school standardized test scores:
"Children with lead at 2 to 5 micrograms per deciliter in their blood -- equal to or below stricter levels of concern set by the federal Centers for Disease Control and Prevention last year -- had a 33% higher likelihood of poor academic performance, said Harolyn Baker, a coauthor of the study and director of epidemiology at the nonprofit Michigan Healthcare Quality Improvement Organization.
"Students with blood lead levels greater than 5 micrograms per deciliter have a 50% chance of doing poorly on MEAP [Michigan Educational Assessment Program] tests, the study found."
Researchers factored out other possible causes of poor test performance related to maternal education, socioeconomic status, race, and gender to make sure that what researchers were seeing was related to lead levels in the blood. "The study updates research highlighted in-depth in the Free Press in 2010. That report found that of 39,199 DPS students tested as young children, only 23 had no lead in their bodies."
Here is a link to The DD News Blog post from May 2010 on the earlier study.