Teachers cannot provide extra student help without more resources, unions say as they call for a nationwide ban on implementing the federal government's new schools agreement.
The Commonwealth has proposed the 10-year Better and Fairer Schools Agreement in a bid to more fairly fund public schools and boost the number of Australian children finishing high school.
It would lift the federal contribution to public schools and provide money for extra support such as catch-up tutoring and wellbeing resources.
But the Australian Education Union says the federal government needs to further increase spending, saying the agreement asks teaching staff to do more without providing adequate resources.
Until all public schools can be fully funded, unionised teacher members across Australia would not carry out the Better and Fairer Schools model, the union's federal president Correna Haythorpe said.
"It's not better and it's not fairer if it's not backed in with funding on the ground," she told reporters in Canberra on Wednesday.
"The situation is untenable."
About two-thirds of Australian students attend public schools, but teachers say government institutions are underfunded in every jurisdiction except the ACT.
The federal government currently provides 20 per cent of each public school's Schooling Resource Standard - which estimates how much total public funding is required to meet students' needs - while most states contribute 75 per cent, leaving a five per cent shortfall.
In a bid to fully fund every public school, the federal government has offered to increase its contribution to 40 per cent in the Northern Territory and 22.5 per cent everywhere else, with the expectation state and territory governments make up the remainder.
Tasmania, Western Australia and the NT have all accepted, but the other states - which are home to the nation's biggest public school systems - have refused to lift their share to 77.5 per cent.
NSW Deputy Premier Prue Car has previously said her state cannot roll out critical interventions at scale without more federal funding.
Victorian counterpart Ben Carroll has hit out at the federal government's refusal to further lift public school funding when it supports private schools to 80 per cent of the Schooling Resource Standard.
Ms Haythorpe has claimed the federal government is in a position to increase its share to 25 per cent.
She also argues teachers in states that have signed on to the agreement still do not have a "full and fair" deal.
This is because a four per cent "additional allowance" can be spent on capital depreciation, regulatory bodies and other non-school costs.
But Federal Education Minister Jason Clare previously noted it would be spent on educational purposes and was part of the Schooling Resource Standard as it covers costs such as school transport.
