SMACKING, long used by parents to discipline naughty children, could cause more than tears.
Research revealed it can also lower a child's IQ, with those smacked up to three times a week having a lower IQ due to psychological stress.
US-based sociologist Professor Murray Straus, who studied the impact of smacking for 40 years, likened the effects of corporal punishment to post-traumatic stress, affecting a child's mental development.
He called on governments to outlaw corporal punishment.
After studying 800 toddlers aged between two and four over a four-year period, he found those who were subjected to smacking had an IQ five points lower than that of a child who wasn't physically disciplined.
"The results of this research have major implications for the well-being of children across the globe," he said.
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"All parents want smart children. This research shows that avoiding smacking and correcting misbehaviour in other ways can help that."
Children aged five to nine years who were smacked regularly had an IQ 2.8 points lower. Dr Straus said children who constantly faced physical punishment lived in fear and suffered stress, which was associated with poorer academic performance.
While not an advocate of smacking, Sydney psychologist Dr Judith Kennedy said parents who gave an occasional tap on the bottom should not fear damaging their child.
"But a child who is suppressed through physical punishment regularly is going to behave differently," Dr Kennedy said.
D) and of course the god old rod.