Children's personal skills are increasingly likely to influence their future earning potential, not just exam results, a think-tank suggests.
After school clubs can boost life skills, the report says
Failure to teach key skills such as communication is widening the gap between rich and poor, says the Institute for Public Policy Research.
It recommends a longer school day so pupils can learn these "soft" skills at after-class arts and sports clubs.
Parents who fail to send their children to clubs should face fines, it says.
The IPPR report is based on surveys with people born in 1958 and 1970.
It found personal and social skills had become 33 times more important in determining earnings over the two generations.
"There have always been class divides in education," IPPR director Nick Pearce said.
"But in the post-war period there were no social class gaps in how children were socialised into developing personal and social skills.
"Now there is a personal skills class divide, and it is contributing in the decrease in social mobility.
"Adolescence is also being stretched at both ends, with children becoming 'teenagers' earlier and 'adults' later."
The IPPR report said social skills could be improved at extra-curricular activities such as the scouts, cadets, martial arts, drama clubs and sports.
The report also called for an "appropriate age limit" be set on TV, newspapers and mobile phone advertising targeted at primary school children.
It added there should be a ban on the promotions ahead of consultation on the issue.
A Department for Education and Skills spokesman said the report raised important issues.
"It is important not to lose perspective and think all teenagers are in crisis - they are not.
"The vast majority of teenagers are achieving more and enjoying more prosperous lives than ever before, as the report acknowledges."
"Youth Matters, our reform of services for young people, has focus on teenagers whose life chances are undermined by disadvantage, support for families in difficulty, and giving all teenagers the skills to seize greater opportunities."