Researchers have found that even jobs such as mowing the lawn, babysitting or doing a paper round can lower maths and science scores for pupils aged 13 or 14. The study of teenagers in 41 countries, to be presented today at the American Sociological Association's annual conference in Chicago, found both paid and unpaid work lowered children's educational achievements.
Boys are particularly at risk of having their education damaged by part- time work eating into study time.
Experts have long believed that working while in school has benefits that cannot be gained from formal schooling - such as increasing a teenager's sense of responsibility, relationships and self image - and allows them to interact with others. However, the new research is worrying for parents and teachers in Britain where there is a growing emphasis on exam results combined with a culture of Saturdays jobs and newspaper rounds for teenagers keen to earn their own money.
David Post, associate professor of education at the University of Pennsylvania, who co-wrote the research, said: "Educators around the world need to be aware of the detrimental effect of working after school on children's education. Boys, and to a lesser extent girls, show substantial negative effects on maths and science achievement, associated with after-school employment."
The researchers took a random sample of secondary school pupils worldwide. The children were asked how many hours a week they worked for pay in their current or most recent job and what type of work they did.
The scientists assessed 26,000 children in the US, who were part of the National Educational Longitudinal Survey, where parents also fill in details about their socio-economic status. More than 400,000 teenagers worldwide, who are participating in the Third International Math and Science Study, which involves 41national school systems, including England and Scotland, were also questioned.
The children were divided into three groups: no paid work; two hours or less of paid work each week and more than two hours of work each week. They were then tested on standard maths and science tests in the eighth grade and then tested again a year later. The findings showed that boys who did not work performed 10 per cent better than those who did regular manual or clerical work and 5 per cent better than those who did occasional work, such asmowing the lawn.
Girls were less affected. They only performed 2 per cent less well if they did odd jobs than those who did not work at all. "The evidence for girls is less dramatic, but still significant," said Dr Post. In Britain boys performed 5 per cent worse if they did paid work rather than non- paid jobs.
"Our research has shown that in most countries, further restricting students' employment would increase student achievement," said Dr Post. "Restricting children's employment benefits not only the wages of adult workers or children's moral or physical safety, but also children's learning and ultimately, a nation's stock of competence in adult workers."
Teenagers taught in large classes do better than those in small groups, researchers have found. They told the conference in Chicago that there is little evidence that smaller classes help to improve results.
Only in American schools did smaller classes help, after exam results were adjusted for socio-economic factors.
Using data from the Third International Math and Science Study, the scientists examined maths standards in Australia, Belgium, Canada, Germany, France, Hong Kong, Korea, Singapore and Iceland as well as the US. Statistics from Britain did not allow researchers to eliminate social and economic factors and were excluded, the researchers said.
The study found class sizes reached as high as 50 in Korea and could be as high as 40 in Singapore and Hong Kong, yet achievement in maths was very high. Dr Suet-ling Pong, of the University of Pennsylvania, told the conference that American pupils studying maths in classes of 6 to 18 did better than those in classes of 19 to 29.Reuse content