I remember reading a very interesting article about a case that showed lead could be a major factor in poor school performance. The article was in a newspaper or news magazine in the '80s or early '90s, and I've not been able to remember enough details to find anything online about it.
Anyway, it was about a school district that had given IQ tests to all the kids. The black kids on average scored significantly lower than the white kids. This could not be explained by the white kids going to better or richer schools, because this district was well integrated. Black kids and white kids that had been together in the same classrooms for their entire school history showed the same IQ gap.
The district concluded that the test was biased and was going to ignore it. One teacher decided to look deeper, and started looking to see if he could find some other factor besides race that was significantly different between the black and white kids.
He realized that all the white kids lived in relatively new housing, and all that black kids lived in much older housing. The black kids' houses were all built long before lead paint was banned. The white kids' house all came after that ban.
They arranged to test the kids for lead, and to test their houses, and they found that most of the black kids were suffering from lead exposure. None of the white kids were.
The lead paint was removed from the black kids' houses, and the kids were treated for lead poisoning.
A couple years later, when the district gave another IQ test, most of the gap between the black and white students was done.