Research from Sussex University based on 17,000 people shows private schooling has little or no effect on people's eventual class or job prospects.
The 18-month study, funded by the Economic and Social Research Council, shows that ability is by far the most important influence on success in life.
It is three times as important as parental class in predicting which social class someone will reach as an adult, and five times as powerful as private education.
In some cases, the study says, the relationship between private education and job prospects is negligible.
The research is the latest contribution to the debate about the role of IQ and social background in determining life chances.
Professor Peter Saunders, the researcher, based his findings on a statistical analysis of the National Child Development Study, which has been monitoring the lives of 17,000 people born in one week in 1958. Their educational attainment and progress were checked at 7, 11, 16, 23 and, most recently, at 33.
Ability was measured by verbal and non-verbal reasoning tests at 11 (similar to IQ tests) and checked against maths and reading test scores at 7, 11 and 16.
Professor Saunders said: "The only strong effect of private education I can find is that it gives people a greater level of confidence at 16. It doesn't have any appreciable effect on exam success."
Sixteen-year-olds who went to private schools had higher aspirations and expectations about their future than those who did not. They were more likely to want to stay on at school and to go to university.
The analysis confirmed that children of parents in professional, managerial and administrative grades (social classes 1 and 2) had three times the chance of reaching these grades.
by the time they were 33 as children born to parents with semi-skilled or unskilled jobs (social classes 1V and V.)
But Professor Saunders challenges the view that the success of the former is based on class or attendance at private schools. Ability is what counts.
He said:"The evidence indicates that recruitment into the middle classes is much more meritocratic than generally believed. If you want to predict where a child will end up on the social ladder, you can make a reasonable prediction on the basis of just three pieces
of information - ability, educational motivation and qualifications."
Downwardly mobile middle class childern had lower test scores than upwardly mobile working class children.
After ability, motivation, measured by a child's attendance record and attitude to studying, was the best predictor of success.
Professor Saunders is now researching other issues that might affect class and occupation such as personality, peer group pressure and social networks. "Some people don't make it because they don't want to," he says.
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