American children whose parents use spanking for discipline have lower IQs than those who aren't spanked, a new study finds. Researchers assessed about 800 2- to 4-year-olds and 700 5- to 9-year-olds and revisited them 4 years later, reporting a dropoff of up to 5 IQ points in kids whose parents engaged in corporal punishment, the Los Angeles Times reports. “The more spanking, the slower the development of the child's mental ability," the lead researcher says. "But even small amounts of spanking made a difference."
The study also found that the populations in countries where spanking is common have lower IQs than in more hands-off nations. The researcher suggests the cause of the disparity is the emotional effect of spanking: It can cause PTSD, which in turn is linked to lower IQ. The US should consider the public health ramifications of spanking, he says, “and eventually enact federal no-spanking legislation.”