Children who were spanked up to the age of six are likely to be more successful in school, more optimistic about life, more likely to take voluntary work, and more keen to attend university than children who were never spanked.

These are the controversial findings from a recent US research study, which has drawn scorn from critics, reported Canadian paper, The National Post.  

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Lead researcher Marjorie Gunnoe, a psychology professor at Michigan's Calvin College, said her study showed that spanking may not always be bad for children.

The findings were drawn from interviews of more than 2,600 people, including a core group of 179 teenagers.

The results were mixed for children spanked between the ages of seven and 11.

Compared to their peers who were never spanked, they rated more highly in terms of their tendency towards violence and anti-social behaviour.

However, they also scored well on positive measures such as academic aspirations, doing well in school and optimism for the future.

Conversely, teenagers above the age of 12 who were still being spanked showed 'clear behavioural problems'.

Mdm Belinda Yuan, President of Aoxiang Counselling Service told Lianhe Wanbao that parents should be strict with their children before the age of 12, but to interfere with them as little as possible after that.

While the effects of rebellious behaviour surfaces at about age 13, the root causes can be found in the child's early development, say child psychologists.

Mdm Yuan says that children start to develop a stronger sense of self when they reach puberty. If parents start to discipline them only then, their kids may misunderstand their good intentions and become even more rebellious.

Dr Ang Yong Guan of Paragon Medical says that five and six are important developmental years, innocent children have yet to be influenced by society, and it is the best time for parents to impart the correct values.

"When children are punished at a young age, they remember the lesson with all their senses, forever searing it into their memory," said Dr Ang, who also emphasized the punishment had to be reasonable and justified.

Mdm Yuan said all punishment had to be fair, and the children should always have a chance to explain themselves. Indiscriminate spanking for minor infractions such as accidentally knocking over a glass of water only strains the parent-child relationship. For example, she thinks that a spanking is justified when children deliberately hurt or attack their peers.

Most importantly, children need to know why they are being spanked, so that they will not repeat their mistakes.

She also suggests that parents not use their hands to spank their children, as they may associate their hands with pain, and misinterpret their parents' gestures of affection in future.