Australia spends more than most countries on education, but class sizes are higher than average, an OECD report has found.
Australia allocated 13.8 per cent of total public spending to education in 2013, compared the OECD average of 11.3 per cent, ranking it fifth out of the 32 countries surveyed in the report.
However, there are three more children per class in Australian primary schools than the OECD average.
The Australian Teaching Union said the higher class sizes indicated schools were under-resourced.
ATU federal president Correna Haythorpe said the report reinforced the Gonski Review's recommendations for needs-based funding, which was adopted by the previous Labor government but substituted by the Coalition.
"This report is more evidence that needs-based funding was necessary to address this bias and reduce achievement gaps between schools," Ms Haythorpe said.
But Education Minister Simon Birmingham said class sizes were not indicative of student performance, and neither was government spending.
"This report from the OECD adds to the facts and evidence that show that, despite many in the community liking the idea of smaller classes, they don't necessarily correlate to better outcomes for students," Mr Birmingham said.
"These new statistics highlight what the Turnbull government has been saying that there is not a clear relationship between education spending and the level of student performance."
China recorded the highest class sizes, averaging almost 50 students in secondary education, while Latvia has less than 20 per class.
The international report also found those with tertiary qualifications earn on average 55 per cent more than those with upper secondary level education.
There is still a large gender disparity with regard to what women study, with Australian women 30 per cent more likely to move into education and humanities than science and engineering.
Australia is among the two thirds of countries that increased expenditure per student between 2008 and 2013, while the report also found Australian high school students spend more time in the class than any other country surveyed.
