Generations of children have been raised on the motto: "Spare the rod and spoil the child."
But a growing body of modern research indicates that corporal punishment may hurt a lot more than the child's bottom.
A new study, involving 17,404 individuals, reveals that children who are routinely spanked tend to score several points lower on IQ tests than those who aren't hit by their parents and guardians.
The lead researcher, Murray Straus, a professor of sociology at the University of New Hampshire and a world authority on the subject, believes spanking may cause so much stress that it interferes with a child's normal learning and cognitive development.
"How often parents spanked made a difference," said Dr. Straus, who presented his findings last week at the International Conference on Violence, Abuse and Trauma in San Diego, Calif.
"The more spanking, the slower the development of the child's mental ability. But even small amounts of spanking made a difference."
Dr. Straus is pleased that both the European Union and the United Nations have called for an end to the corporal punishment of children. So far, 24 countries have introduced legislation that bans spanking.
In Canada, the Supreme Court has upheld a law that permits parents and caregivers to use "reasonable force" when disciplining children over the age of 2.
But even in countries that haven't prohibited spanking, the practice seems to be on the wane. And Dr. Straus thinks that bodes well for future IQ gains around the globe.