An article in National Geographic by Yudhijit Bhattacharjee: In the late 1980s, when the crack cocaine epidemic was ravaging America's cities, Hallam Hurt, a neonatologist in Philadelphia, worried about the damage being done to children born to addicted mothers. She and her colleagues, studying children from low-income families, compared four-year-olds who'd been exposed to the drug with those who hadn't. They couldn't find any significant differences. Instead, what they discovered was that in both groups the children's IQs were much lower than average. "These little children were coming in cute as buttons, and yet their IQs were like 82 and 83," Hurt says. "Average IQ is 100. It was shocking."
The revelation prompted the researchers to turn their focus from what differentiated the two groups toward what they had in common: being raised in poverty. To understand the children's environment, the researchers visited their homes with a checklist. They asked if the parents had at least ten books at home for the children, a record player with songs for them, and toys to help them learn numbers. They noted whether the parents spoke to the children in an affectionate voice, spent time answering their questions, and hugged, kissed, and praised them.