Children who are smacked are more aggressive and have poorer mental development than those who are verbally castigated, studies have found.
Research on toddlers and other studies following children into adolescence found physical punishment was bad for children and made them more likely to show anti-social behaviour.
The children who were smacked at age one were more aggressive and had not developed cognitive skills as well as those punished verbally.
In a separate study children aged between five and 16 found that children who were spanked often were two to three times more likely to show anti-social behaviour than those not punished physically.
The findings are likely to reignite the debate on whether it is right for parents to smack their children.
In Britain mild smacking is allowed under a "reasonable chastisement" defence against common assault.
But any punishment which causes visible bruising, grazes, scratches, minor swellings or cuts can result in a prosecution for assault occasioning actual bodily harm, or more serious charges.
Last year a cross-party group of MPs failed to force through a ban in England and Wales on smacking children after there was just four hours to debate legislation in the Commons.
The latest research conducted in America has found that smacking young children affected their behaviour and their mental development.
In one study 2,500 families with children aged one, two and three recorded how often they were smacked and used recognised systems to measure their behaviour and mental skills.
Around one third of one-year-old children were spanked and received on average more than two spankings a week – defined as hitting with an open hand on the buttocks or other extremity.
Half of two-year-old were punished physically, receiving almost three spankings a week on average. The rate was similar for three-year-olds.
The findings show children who were spanked more often at age one behaved more aggressively when they were two and had lower scores on tests measuring thinking skills when they were three.
Dr Lisa Berlin, research scientist at the Centre for Child and Family Policy at Duke University in North Carolina, said: "Our findings clearly indicate that spanking affects children's development."
The study was conducted by researchers at Duke University, the University of Missouri-Columbia, the University of South Carolina, Columbia University, Harvard University, and the University of North Carolina at Chapel Hill and was published in journal Child Development.
The findings remained significant after factors such as race, ethnicity, age, education, income and the child's gender, were taken into account.
Verbal punishment alone did not affect either children's aggression or their cognitive development, Dr Berlin said.
Dr Berlin said the study examined if children who were more aggressive elicited more spanking and they did not. She said this meant that 'although children’s characteristics always play a role, our findings emphasise the influence of parenting on child behavior and development'.
Another study in the same journal looked at the long-term effect of physical punishment on children as they grew up into teenagers.
A total of 750 children aged between five and 16 were studied and it was found that parents generally reduce physical punishment as the child gets older.
But in families where the physical punishment continued the children were more likely to have behaviour problems than those who never spanked them or who stopped spanking them when they were still young.
Dr Jennifer Lansford, associate research professor with the Social Science Research Institute and Center for Child and Family Policy at Duke University, who led the study, said children who were exposed to physical discipline most frequently were two to three times more likely to show anti-social behaviour as an adolescent, including things like getting into fights, being disobedient at home or at school, general delinquency and being in trouble with teachers.
High levels of physical punishment was defined in the study as spanking once a month, she said.
It was found that if spanking stopped by age nine the child was no more likely to show anti-social behaviour as an adolescent than if they had never been spanked.
Dr Lansford said: "Given these findings, mental health specialists and others who work with families should encourage parents to refrain from using physical discipline.
"They should also help parents come up with alternate strategies for disciplining their children.
"Parents are also more likely to continue using physical discipline with children who behave aggressively."
John Dunford, general secretary of the Association of School and College Leaders, said corporal punishment in schools never worked because the same names would appear time and again in the punishment book.
He said: "It seems highly likely that children exposed to violence would themselves use violence in reaction to situations. Violence begets violence is a lesson from history not just child psychology."
Source: Telegraph.co.uk – http://tinyurl.com/oxr2yp
