Angry parents, the next time you inflict corporal punishment on your kid, give a second thought for a new study says that smacked children have lower IQ.

Researchers at New Hampshire University have carried out the study and found that children who are smacked by their parents are less intelligent than their classmates, The Daily Telegraph reported.

What’s more shocking is that the study has also found a link between how often children are punished and their IQ.

And, according to the researchers, children who are regularly smacked can suffer symptoms more closely associated with post-traumatic stress disorder, including becoming more fearful and easily startled.

Lead researcher Prof. Murray Straus said: “How often parents spanked made a difference. The more the spanking the slower the development of a child’s mental ability. Even small amounts of spanking made a difference.”

For their study, the researchers analysed more than 1,500 children split into two groups, the first aged between two and four and the second aged between five and nine.

They recorded how often the children were smacked by their parents over four years and then tested their intelligence. They found the IQ of those in the younger age groups was an average of five points lower if they had been spanked than if they had not.

Similarly for the older children, the study found that their average IQ was 2.8 points lower if they were spanked.

Average IQs are lower in countries where there are high levels of parental smacking than in those where it has been banned, according to the researchers who are to present their findings at ‘International Conference on Violence, Abuse and Trauma’ in San Diego.