It was the children of a healthy birth weight, who grew up in higher socio-economic circumstances in homes filled with books and had mothers who didn't work long hours who performed best at NAPLAN.

The study authors said their findings, to be presented at a conference next month, debunked conventional wisdom that ''private schooling enables children to achieve better academic results''.

''We found that NAPLAN test scores … of students from Catholic and other private schools did not statistically differ from those in public schools,'' the authors said.

''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.''

For the study, the University of Queensland researchers matched the 2008 and 2010 NAPLAN results of 15,000 year 5 students and 11,000 year 3 students with data from a long-term study that is tracking Australian children from age four.

After controlling for factors like household income, health indicators and parent education level, researchers found there was no statistical difference in the academic achievement of children from similar backgrounds, regardless of which type of school they attended.

''People who are sending their kids to public schools can be confident they're not disadvantaging their kids by doing so,'' one of the researchers, professor of health economics Luke Connelly, said.

''It's not the type of school that changes [the result], it's the things that are being done for the child at home.''

But Professor Connelly said that didn't mean parents paying for primary school education were wasting their money. ''This is one measure of school performance. It's not indicative of the overall value of the school experience for kids and parents.''

Two-thirds of the children in the study attended public schools, while 20 per cent were educated in the Catholic system and the rest at independent schools.

Researchers found that compared with NSW children, Victorian children performed better at reading, and Queensland children performed better at numeracy. All the other states consistently recorded lower test results than NSW in NAPLAN.

Children who weighed less than 2.5 kilograms at birth achieved ''significantly lower'' test scores, especially in grammar and numeracy, with the researchers suggesting low birth weight correlated with longer term developmental delays.

Children whose parents had completed year 12 had significantly higher test scores across all subjects. Students whose mothers worked long hours did worse in all tests except numeracy.

''One explanation for this may be that children of young ages typically spend more time with mothers than fathers; perhaps mothers who work long hours make greater sacrifices of the amount of parental time their children receive,'' the study authors said.

Researchers found year 5 students attending Catholic schools performed significantly worse than those at public schools in all subjects except reading and writing.

However, Professor Connelly said they would have to wait to see how this cohort performed in year 7 before drawing conclusions.

Public pick for primary

Although she was privately educated herself, Lilyfield mother Amy Miller has deliberately chosen to send her daughter Isabella to a public primary school.

Better resources do not always equal a better education.

''You have to drill down into the education at the school, it's really individual. It comes down to the teachers, their programs, what the focus is,'' she said.

Ms Miller said she wouldn't have considered anything other than the local public primary school for Isabella. ''It's her first experience of school; it's great to be part of the local community. Kids in our street go to the local school. There is an element of unity that comes from [going to the local public school] when you're in a suburb with those like-minded parents and kids.''

But the choice of Annandale North Public for Isabella had nothing to do with the school's NAPLAN results. ''I was purely hoping that for at least a few years she'll be happy and enjoy where she is, that she'll find friends and have nice teachers that make her feel confident,'' she said.

The private versus public school debate was coming up a lot in discussions with parents, Ms Miller said, as they started thinking high school. ''There's this real confidence in people that you just can't go wrong when you're at a private school,'' she said.

Ms Miller said she and her husband could not afford private school fees for high school. She is weighing up a few nearby Catholic girls' high schools and some of the local public schools. She likes the idea of single sex education in high school, and suspects the Catholic schools may have more resources.

smh.com.au