BBC News science reporter, Dublin, 8 September 2005
By Jonathan Amos
It puts some numbers behind what teachers have long thought .
The naughty boy at primary school who continues to muck about even after being told off may have completely missed his teacher's displeasure.
The suggestion comes from new research that gives scientists an insight into the differences in "wiring" in young male and female brains.
It seems many school-entry boys have greater difficulty picking up on some emotions, such as anger.
Understanding these differences could be useful in class, scientists said.
"If teachers attempt to control boys by subtle means, such as raised eyebrows, and the boys ignore these cues, it may be that they simply are not able to read them and decode them accurately," explained Professor David Skuse, whose team at the Institute of Child Health in London conducted the research.
"It's not that they are being wilfully oppositional," he told the British Association's Festival of Science, which this year is being held in Dublin, Ireland.
The study on 600 children between the ages of six and 17 was actually undertaken to investigate aspects of autism, a predominantly male condition.
The institute hopes eventually to find the genetic factors that lead more boys than girls into this disorder.
The experiments used a series of computer-based tasks that required children to interpret emotional expressions on faces - happiness, sadness, disgust, anger, fear and surprise.
They also had to remember faces and to follow eye gaze - the sorts of abilities often found wanting in autistic individuals.
The results showed that although there were early sex differences, with girls doing significantly better than boys at the time of school-entry, these differences reduced over time. And by late adolescence, they were all but gone.
The differences at school-entry were specifically to do with the facial expressions tasks.
"At six years, 70% of boys are below the mean for girls; so in other words, 70% of boys are worse than 50% of girls," Professor Skuse explained.
"It means there are a lot of boys at school-entry who are very poor at differentiating other people's emotions from their facial expressions.
"This perhaps wouldn't come as any surprise to teachers to whom I've spoken about this finding - they say boys are less socially aware when they enter school - but I think this is the first objective evidence that there is a substantial difference between the sexes in the ability to read these emotions."
One fascinating observation was that both boys and girls in their early teenage years experienced a dip in their ability to perform some of the tasks.
This, Professor Skuse speculated, was probably because their brains were being rewired at that time.
But he raised the suggestion - slightly tongue in cheek - it could explain the "Kevin factor", a reference to the unruly behaviour of the TV teenage character made famous by comedian Harry Enfield.
"I'm suggesting in a fairly light-hearted way that the social ineptness of early adolescence, the seeming inability to understand the expressions of sadness and anger, would appear to be just a function of the development of their brain at that time.
"It's not a cultural phenomenon, I suggest; it's a real biological phenomenon from which they, fortunately, recover." The research is to be published in the Journal of Applied Statistics.