MELBOURNE, Oct 10 - The Australian Education Union says the huge jump is because Victoria's independent schools are claiming a full quarter of their students have a disability.

Disability loadings for Victorian independent schools will increase from $63.7 million in 2017 to $123.3 million in 2018, but it will drop $16 million for Catholic schools, figures obtained union under freedom of information show.

That means 55.8 per cent of the total national increase for disability education will go to independent schools in Victoria, while public schools will only increase by 11 per cent.

"They are concentrating a miserly funding increase among wealthy private schools that are suddenly reporting a big unexplained rise in their claimed numbers of children with a disability," Correna Haythorpe, AEU Federal President said in a statement on Tuesday.

"'We need an explanation, and that may only come with an independent audit of what appears to be a further gold-plating of the private system at the expense of children in public schools."

The union says it has seen a confidential report that shows Victorian independent schools are reporting 26 per cent of their students have a disability.

That's compared with 17 per cent for Victorian public schools, and 13 per cent for Victorian Catholic schools.

Because the small national funding increase is being spread across such a large number of students in all sectors, disability funding for public schools is being cut in five states and territories, the union says.

Catholic Education Melbourne says national disability assessments are allowing schools to "game the system" by relying on "teacherjudgment" and inconsistent data collection.

"[Education Minister Simon] Birmingham's new funding approach effectively allows schools to write their own cheques," CEM executive director Stephen Elder said.

"It seems from the data collected to date that some independent schools have written themselves very large cheques indeed.

"It strains credulity to say that one in four students in independent schools in Victoria has a disability."