A global report on educational performance shows Australian 15-year-olds are getting worse at maths, science and reading.
About half a million students from 72 countries took part in the Programme for International Student Assessment (PISA) 2015, including more than 14,000 Australian children.
Australia was significantly outperformed by nine countries, ranking just below New Zealand, well below Japan and Canada, and just above the United Kingdom and Germany.
Singapore's students ranked highest.
Dr Sue Thompson from the Australian Council for Education Research collected the Australian data and said local academic performance was in "absolute decline".
"The proportion of high achievers is decreasing and the proportion of low achievers is increasing," she said.
"Basically what's happening there is everything's sliding backwards if you like — our strong kids aren't as strong as they were and our weak kids are actually weaker than they were."
Federal Education Minister Simon Birmingham said the country could not afford to "continue to slip behind".
"Our children are no longer learning at the same rates through their school education as they used to and that is obviously unacceptable to governments, as it would be to parents, teachers and everybody across Australia," he said.
NT AND TASMANIA BELOW OECD AVERAGE
The Australian Capital Territory topped the rankings with Western Australia not far behind but NT and Tasmania were below the OECD average .
OECD countries including places like Canada, Netherlands, New Zealand, the UK and the USA. Worryingly state schools are falling behind private schools too.
"This is not surprising," Australian Education Union's deputy federal president Maurie Mulheron said.
"The Gonski review said this is exactly what would happen."
"[The Gonski review] said that if we did not act as a nation to redress the imbalance between advantaged and disadvantaged students then we would slip down in international ranking," he said.
The gap between rich and poor schools were what the Gonski model was supposed to fix, Opposition education spokeswoman Tanya Plibersek said.
"Our results have become worse as our education system has become more inequitable," she said.
Mr Birmingham said school funding had gone up to record levels "yet performance has gone backwards".
"It really is time to end the politicking about money," (There’s a surprise! It’s not the failure to deliver Gonski or our real cuts to state education funding…Let me guess, it’s the teachers and the unions!)
OCOS Are asking for some re-thinking come state budget time.