Children's happiness is far more strongly influenced by family conflict than by factors such as living in a single parent household, according to the findings of a study published yesterday.

Research by the Children's Society showed seven per cent of children aged between 10 and 15 in England - around 300,000 - are "significantly" unhappy, with family rows a major cause of dissatisfaction with life.

Children who report that their family "gets along well together" are on average around 20 per cent happier than those who do not, regardless of whether they have a lone parent, or step-families, or live with both birth parents, the study found.

The impact of family conflict on children's well-being far outstripped family structure, with a child in a lone parent household two per cent unhappier than one living with both birth parents, the report found.

The study of the views of nearly 7,000 children, carried out in collaboration with the University of York, found the vast majority were happy, placing themselves above the mid-point measure on a happiness scale ranked from one to 10.

But the research showed that of the 6,744 children interviewed in year six, the final year of primary school and years eight and 10 of secondary school, an average of two in every class were unhappy.

The seven per cent of "significantly" unhappy children amounted to 140,000 out of the 1.8 million children in the three year groups, or 300,000 if all 10 to 15-year-olds were counted, the charity said.

The survey, carried out by Ipsos Mori, asked children to give a score out of 10 on a happiness scale to a series of aspects of their lives.

The highest average marks - of nearly nine out of 10 - were given for happiness with home, friends and family.

The highest levels of unhappiness were recorded in areas of appearance and confidence, with 17.5 per cent saying they were unhappy with their looks, and 16 per cent unhappy with their confidence. Almost twice as many girls were unhappy with their appearance as boys.

Nearly 14 per cent were unhappy about the area they live in and just over 13 per cent about the school they attend, with nearly 12 per cent unhappy about their school work.

Almost 11 per cent said they were unhappy with the amount of choice they have in life and 10.5 per cent unhappy about the amount of freedom they have.

Just over 10 per cent were unhappy about what may happen to them later in life.

The average "well-being" score was 7.7 out of 10, the study found.

But happiness levels fell as children got older, with average happiness scores falling from around eight out of 10 in the last year of primary school to around 7.4 for young people aged 14 to 15 years old.

Between these age groups, happiness with many aspects of life such as family relationships and school also fell but happiness with friendships remained stable.

Boys tended to be happier than girls with the gap in well-being increasing with age, the research found.

Among the 14 to 15 year old age group, girls' average well-being was 7.2 out of 10 compared with 7.6 for boys.

The findings have been released a year on from the publication of the Good Childhood Inquiry, a landmark independent report into modern childhood commissioned by the Children's Society.

The charity said the aim of the research project, believed to be the biggest of its kind, was to create a "well-being index" to inform and measure the impact of public policy and track changes in children's happiness.

Bob Reitemeier, chief executive officer of the Children's Society, said: "This ground-breaking study is a major step forward in our efforts to understand and enhance the well-being of young people.

"It shows the vast majority of our children are happy, but it is a major concern that two children in every classroom are unhappy, and that so many are insecure about their appearance and confidence.

"Family conflict emerges in this study as a major cause of childhood unhappiness, and so it is vital that families can get the sort of family mediation and counselling the Children's Society offers to help them resolve and avoid conflicts.

"This report is a stark reminder that our actions as adults can have a profound impact on our children's well-being and the importance of listening to what children are telling us."

Survey co-author Professor Jonathan Bradshaw, of the University of York, said: "This survey makes a major contribution to our understanding of children's subjective well-being in England and the factors that contribute to it."