Girls are less happy with their lives than boys - and the nation's obsession with body image is to blame.
According to David Cameron's project to measure the nation's 'well-being', almost one in three girls aged 11 to 15 struggle with their appearance. Boys, too, are affected, but not to the extent of girls.
The figures are being blamed on 'airbrush' culture which is leaving children struggling to separate real life from an ideal.
As part of a wider survey of households, secondary school-aged children were asked to rate how happy they felt about life in general on a scale of one to seven.
They were then asked to rate how they felt about their friends, family, school, school work and their appearance on the same scale.
In total 94 per cent of both boys and girls described themselves as at least generally happy in their family.
When it came to their friends the figures were 96 per cent and 95 per cent respectively.
When asked about their school work 85 per cent of girls and 79 per cent of boys were happy.
But when questioned about their appearance, only 71 per cent of girls said they were even moderately happy.
Among boys 80 per cent said they were happy with their appearance.
Sue Palmer, author of the book Toxic Childhood, told the Telegraph that advertising and social media sites were drawing girls in particular into 'tween' culture earlier and earlier.
"Children are encouraged, through commercial influence, to become more and more self conscious about what they look like, what they are wearing and how they appear," she said.
"We have reached saturation point with image and the images children feel they have to live up to are so unrealistic in comparison with human beings.
"I wonder sometimes whether children see more screen based images of people than they do real life people on an average day. They are being bombarded with images and often they are images of a physical perfection you could never live up to."
She said that the growing requirement to live a virtual life on screen meant children would inevitably be tempted to airbrush their own pictures.
"What is happening now with social networking sites and everything being so visual is that girls feel that they are now responsible for a personal PR campaign," she said.