Catholic school principals say a new online calculator giving parents details of the Turnbull government's new schools funding package has only led to more confusion.
Prime Minister Malcolm Turnbull was heralding the new estimator in parliament, which allows parents and schools to see how much they stand to win or lose.
"It is transparent," he said on Tuesday.
But Catholic schools are having trouble reconciling the results from the estimator with the letters and figures they've received from Education Minister Simon Birmingham.
"That has led to significant confusion, which is adding to the anxiety Catholic schools are facing as the Turnbull government seeks to change the way Australian schools are funded," National Catholic Education Commission's acting executive director Danielle Cronin told AAP.
Ms Cronin warns parents will also be confused by the data, which doesn't include other important sources of funding for schools.
The existing 'MySchool' website providesamoreaccuratepicture,albeit retrospectively, becauseitincludesfundingfromCommonwealthand stategovernments,as wellasfees, she said.
Catholic Education Melbourne's executive director Stephen Elder described the estimator as an "omnishambles" for the government.
The figures confirm 24 independent schools will have their funding cut in real terms over the next four years, and another 27 Catholic schools in Canberra will either have cuts or freezes.
However, all but 251 of the nation's 9400 schools will have their funding grow by at least 2.5 per cent, with 4500 getting a more than a five per cent boost.
Mr Turnbull defended the package during question time, saying while Labor had 27 "special deals" the coalition was delivering a national needs-based system.
He also questioned why Labor has failed to promise to put back $22 billion in funding it argues schools would have received under the opposition.
"It was a promise that mocked Australian schools," he said.
Earlier backbenchers agreed to the plans - labelled Gonski 2.0 - despite the concerns of the Catholic sector and Tony Abbott and Kevin Andrews voicing theirs.
Mr Abbott told colleagues he thought it was a mistake to embrace David Gonski - noting he was Julia Gillard's advisor - and his principles, while Mr Andrews said the "devil was in the detail".
Liberal senator Zed Seselja told hundreds of Catholic parents at a meeting in Canberra on Monday night he had put their concerns to Senator Birmingham "very forcefully".
Senator Seselja - a product of Canberra's Catholic school system - where his children are also enrolled - said while they were very good schools, they were not elite.
But Labor has questioned whether a junior minister's promise to Catholic parents will address their concerns about the funding model.
"I think if a chat from Zed Seselja was going to fix it, it would have been fixed by now," opposition education spokeswoman Tanya Plibersek said.
Senator Birmingham told parliament he had numerous meetings with representatives from the Catholic sector.
Legislation for the funding is expected to be put to parliament later this week, with the Greens planning to refer it to a Senate inquiry.
SCHOOLS THAT LOSE MONEY
* Loreto Kirribilli (NSW)
* Monte Sant' Angelo Mercy College (NSW)
* St Aloysius' College (NSW)
* St Pius X College (NSW)
* Mount St Benedict College (Pennant Hills - NSW)
* Daramalan College (ACT)
* Hillbrook Anglican School (Queensland)
* Radford College (ACT)
* Burgmann Anglican School (ACT)
* Marist College Canberra (ACT)
* Brigidine College, St Ives (NSW)
* Brindabella Christian College (ACT)
* Stella Maris College Manly (NSW)
* Oakhill College Castle Hill (NSW)
* Covenant Christian School (NSW)
* Waverley College (NSW)
* St Scholastica's College (NSW)
* Northern Beaches Christian School (NSW)
* Masada College High School (NSW)
* Cannon Hill Anglican College (Queensland)
* Inner Sydney Montessori School (NSW)
* Orana Steiner School (ACT)
* St Augustine's College (NSW)
* St Edmund's College (ACT)