Parents the world over are in no doubt that sending their children to private school will improve their life chances, thanks to the smaller class sizes, individual attention and better facilities on offer.

But researchers behind a new study of primary school exam results have claimed that students who attend private schools do not actually perform better than their peers in the state sector.

Factors such as a child’s birthweight, their socio-economic status and even the number of hours their mother worked were found to be far more effective predictors of academic attainment than the type of school they attended.

The research, carried out in Australia by academics from the University of Queensland, analysed the results of 26,000 students in Year 3 (aged 8-9) and Year 5 (aged 10-11) in national tests. Two-thirds of the children attended state schools, 20 per cent went to private Catholic schools and the rest were at other private schools.

In terms of raw results, students attending private schools appeared to perform better than their state school counterparts, with those attending Catholic schools coming out top.

However, after taking the impact of variables such as household income, health and parental education into account, researchers found that there was little statistical difference in the academic achievement of children from similar backgrounds, irrespective of what type of school they attended.

“We found that (national) test scores ... of students from Catholic and other private schools did not statistically differ from those in public schools,” the report says. “Our finding seems to suggest that ‘nature’ provides a more consistent role than ‘nurture’ at affecting children’s cognitive outcome in this young age group.”

“Significantly lower” test scores were achieved by children who weighed less than 2.5kg (5lb 8oz) at birth, an outcome that the researchers believed could have resulted from related developmental delays.

Students whose mothers worked longer hours also tended to struggle. Children whose parents had stayed in school until the age of 18, however, achieved significantly higher test scores.

The authors argued that their findings debunked conventional wisdom that “private schooling enables children to achieve better academic results”.

“People who are sending their kids to (state) schools can be confident they’re not disadvantaging their kids by doing so,” Luke Connelly, professor of health economics and one of the academics behind the research, told The Sydney Morning Herald. “It’s not the type of school that changes (the result), it’s the things that are being done for the child at home.”

This view is supported by US husband and wife Christopher and Sarah Lubienski, who are professors in the College of Education at the University of Illinois at Urbana-Champaign.

Their new book The Public School Advantage: why public schools outperform private schools argues that, when social factors are stripped out, US state schools outperform those in the private sector.

Influential American educationalist and author Dianne Ravitch has praised the book for providing “clear evidence that the free-market model of schooling does not match the hype of the privatisation movement”.

“It demonstrates that public education is a valuable and successful institution. It must be protected and strengthened, not privatised,” she said.

In the UK, successive governments have called on private schools to do more to support state education, promoting the idea that state schools would benefit from taking on the “DNA” of the private sector. Private schools have come under intense political pressure to sponsor autonomous, state-funded academies and to partner with local state schools.

But Professor Alan Smithers, director of the Centre for Education and Employment Research at the University of Buckingham in England, disputed the study’s conclusion that private schooling does little to improve educational chances.

“This is good research, but not good advice,” he said. “This looks to me like an attempt to explain the differences (in attainment) between private and state schools. There is a big difference in outcomes, although this can be explained by the difference in (schools’) intake.

“This is interesting from a research point of view, but it doesn’t alter the fact that the independent schools do have the best results.”