A psychiatrist who studies violence and trauma has revealed the results of a long-range study of the intelligence of children who were spanked. Murray Straus of the University of New Hampshire says that even a little spanking adversely affects the intelligence of the children years after the event.

According to Science Blog:

Straus found that children in the United States who were spanked had lower IQs four years later than those who were not spanked.

Straus and Mallie Paschall, senior research scientist at the Pacific Institute for Research and Evaluation, studied nationally representative samples of 806 children ages 2 to 4, and 704 ages 5 to 9. Both groups were retested four years later.

IQs of children ages 2 to 4 who were not spanked were 5 points higher four years later than the IQs of those who were spanked. The IQs of children ages 5 to 9 years old who were not spanked were 2.8 points higher four years later than the IQs of children the same age who were spanked.

"How often parents spanked made a difference. The more spanking the, the slower the development of the child's mental ability. But even small amounts of spanking made a difference," Straus says.

via Science Blog