A robust body of evidence suggests that spanking or smacking a child leads to problems – and the latest evidence shows it can cause increased levels of aggression and worse vocabulary skills in children.
Researchers from Columbia University in the US came to the conclusion after analysing data collected from 1500 families, and the study has been published this week in the journal Pediatrics.
While several studies have found a connection between spanking and aggressive behaviour, the finding that smacking could be linked to cognitive ability, including language skills, was somewhat new.
"Only a few studies have looked at the cognitive effects of spanking," said Michael MacKenzie, an associate professor at Columbia University and lead author of the study.
"We are still trying to learn if spanking has a direct effect on early brain development, or if families that spank more are less likely to read to their kids and use more complex language."
In this latest study, 1500 families were tracked from their child’s birth through to age 10. Parents were asked about their child's behaviour and whether they had smacked their children within the past month.
The answer was frequently yes: 57 per cent of mothers and 40 per cent of fathers reported spanking their kids at age three, and did 52 per cent of mothers and 33 per cent of fathers when their children were five.
When these kids turned nine, parents were asked to assess their behaviour. The researchers also gave the children a test that measured their vocabulary.
The FFCW study also collected other data that might influence a nine-year-old's behaviour and performance on the vocabulary test, including the age of the mother when the child was born, the mother's self-reported stress levels, her intelligence scores, and her own impulsivity.
The researchers also knew whether the child had a low birth weight and what his or her temperament was like during the first year of life, among other things, and factored all these into their analysis.
"If you were just to compare kids who were spanked and not spanked, the differences may not relate to the spanking, because the families that do spank may look different from non-spanking families in lots of ways," said MacKenzie.
But even when the researchers controlled for these differences, "we still saw that spanking is an influencing factor in future behaviours".
The researchers found a clear connection between smacking at age five and the child's behaviour at age nine.
Compared to children who were never smacked by their mothers, those who were smacked at least twice a week scored 2.66 points higher on a test of aggression and rule-breaking, while those who were spanked less frequently scored 1.17 points higher, according to the study.
To get a sense of how much extra aggression that was, boys tended to score one point higher on this test than girls, MacKenzie said.
The effects of spanking by fathers were different. Compared with children who were never smacked by their dads, those who were spanked at least twice a week scored 5.7 points lower on a vocabulary test, the researchers found.
To put that in perspective, MacKenzie noted that children whose mothers dropped out of high school score 2.6 points lower on this test, on average, than children whose mothers finished college.
MacKenzie believed that this research showed a need for public health officials and pediatricians to re-examine how they were talking about spanking.
"Spanking is still the typical experience for most kids," he said.
"We have to start being more thoughtful about how we present this information for parents in a way that they can receive it."
So many parents have a hard time accepting that smacking is truly bad for kids, probably because they were smacked as children and think they turned out okay, he said.
"The decision to spank is tied to most parents' own rearing experiences," said MacKenzie.
"It is intimately tied to family history."