LEIGH SALES, PRESENTER: The Prime Minister is fast approaching D-day on his schools funding plan. It could come as soon as tomorrow, if his Education Minister can pull together some concessions to satisfy concerns inside and outside the Coalition party room.

The powerful teacher's union is trying hard to block it, even though one of its former presidents says the bill should pass in the interests of public education.

Political correspondent, Andrew Probyn takes a look and finds that politics is more at play than policy.

SIMON BIRMINGHAM: Seems you were here yesterday morning, some of us.

REPORTER: Deja vu.

SIMON BIRMINGHAM: Exactly.

ANDREW PROBYN, POLITICAL CORRESPONDENT: Deja vu? You can say that again.

The Catholic school sector has brought a Federal Government to its knees before, all over a toilet block.

ARCHIVAL NEWS FOOTAGE: This lavatory was condemned as being unsuitable and too small for the number of pupils attending this school. The health departments and the education department demanded that it be renovated but the Catholic bishop here said that they couldn't afford to and asked the state to help.

The answer was no.

ANDREW PROBYN: It was 1962, and Goulburn's seven Catholic schools shut their gates, leaving 2,000 students to descend on six public schools.

The strike worked.

ROBERT MENZIES, FMR PRIME MINISTER: We must all thank God that the work of the church goes on.

ANDREW PROBYN: Prime Minister Robert Menzies introduced state aid for Catholic schools, despite Labor opposition, but by 1969, with the Catholic vote bleeding to the conservatives, Labor leader Gough Whitlam engineered a reversal of this position and state aid became bipartisan policy.

QUESTIONER (Archival): One question, how long are our kids going to remain second class citizens in this country.

ANDREW PROBYN: Fast forward 50 years, and the Catholic school sector still remains powerful.

EXTRACT FROM AN ADVERTISEMENT: The Department of Education said that Catholic schools will be $4.6 billion worse off over the next decade.

ANDREW PROBYN: That kind of campaign has found its target, and the Prime Minister is facing the prospect of MPs crossing the floor.

Malcolm Turnbull today reminded them the so-called Gonski 2.0 was agreed to by the party room some weeks ago, but that didn't stop several voicing concerns, including Tony Abbott, Kevin Andrews and retiring Senator Chris Back.

SARAH HENDERSON, LIBERAL MP: Look obviously, some members have different views, but fundamentally there is very strong support for our program of ensuring that every single Australian child receives the funding they need.

ANDREW PROBYN: Liberal MP Sarah Henderson worries that in the flurry of claim and counter-claim, the beneficiaries are being forgotten.

SARAH HENDERSON: I look at my own electorate, Andrew, in Corangamite, schools like Trinity College in Colac are receiving an amazing boom of funding, an extra $20 million.

So particularly in rural and regional areas of Australia, where there is some inherent disadvantage, this is a huge funding boost for Australian schools.

ANDREW PROBYN: The Government will resist doing any detail with the Catholics that unpicks the seams of the entire schools funding package.

To that end, any concession the Catholic sector gets will likely be offered to other non-government schools to stop walkouts.

A bit like the 1960s, it's about containing the prospect of a sectarian spat.

But this is about a schools funding method that has split the Catholic and private sectors. If the Government offers the Catholics a 12 month extension of the existing funding system, it would aggravate the non-Catholic private schools which prefer the new system.

As for the Labor-aligned Education Union, which represents public school teachers, it remains opposed, to the dismay of its former president.

DIANNE FOGGO, FMR PRESIDENT, AUSTRALIAN EDUCATION UNION: I've had decades of activism and passion about supporting public education, and I am absolutely terrified if this chance goes past, it will be many decades again before there's an opportunity to get needs-based funding for public schools in Australia.

ANDREW PROBYN: Dianne Foggo was federal president of the Australian Education Union for five years. She has written to her old union, political leaders and the crossbench, urging them to support the reforms.

DIANNE FOGGO: It's not perfect. The first Gonski report was the one that should've been implemented and it wasn't and this is not as good but it provides an amazing opportunity for the future of public education in this country, and I just couldn't let this go by without saying something, and hoping that people would with my background listen to my views.

ANDREW PROBYN: Labor could back the model she says, and still offer greater funding.

DIANNE FOGGO: If Labor as good as its word, when it gets into government, it has the opportunity then on a needs based funding model to put the funds that they so desperately want to go into education. And so, perfect never works. No-one can achieve perfection but this is a very, very decent step forward.

ANDREW PROBYN: As we wait to see whether the Government dares put up the legislation for a Senate vote tomorrow, the scrap in Question Time continued.

BILL SHORTEN, OPPOSITION LEADER: Will the Prime Minister finally admit that his schools policy is a train wreck? Public schools hate it, Catholic schools hate it, and it's Government's own members despise it.

TANYA PLIBERSEK, SHADOW EDUCATION MINISTER: Isn't it the case that any changes the Prime Minister wants to make to his school cut package have nothing to do with the children and everything to do with appeasing the members for Warringah, Menzies, Dawson, Senator Back, Senator Abetz and Senator Sarah Hanson-Young?

MALCOLM TURNBULL, PRIME MINISTER: Every element of our school funding package is focused on the needs of Australian children.

The money is there, the commitment is there, the needs-based funding is there. Labor's politics will not distract us from delivering for Australian children. Our children deserve better.

ANDREW PROBYN: The future of the schools funding plan is in the balance. Malcolm Turnbull told colleagues today the Government needs a strong finish to the week.

But no-one needs a big win more than the Prime Minister. Going into the winter recess without his school reform sewn up could have longer term consequences on his leadership.

It's a high stakes game and the PM must ensure any concession does not harm the integrity of a system that aims to direct funding where it's most needed. Otherwise, what would be the point?

DIANNE FOGGO: I just implore people to put aside their differences, to put in a reasonable model, have it in law and then work to improve it later.

Don't throw the whole thing away now because it's not perfect.