The State Opposition says it has obtained documents that reveal almost 600 teaching positions could be slashed as part of the Government's overhaul of the education sector.

In Parliament, the Opposition Leader Mark McGowan produced a Department of Education document outlining changes to the current allocation of teaching positions in state schools.

It includes plans to change the base teacher allocation rate, as well as altering the formula used to calculate student-to-teacher ratios for years 8 to 12.

Mr McGowan estimates the changes will slash about 585 teaching positions

"Mr Collier and Mr Barnett said no teaching jobs will be lost, there will be hundreds of full time equivalent jobs lost by changes to the formula,"

It comes after last month's announcement the government would slash 500 department and education assistant jobs across the sector.

The Government has maintained no teachers will lose their jobs.

Meanwhile the Premier Colin Barnett stepped up his attack on the State School Teachers' Union, saying it made a big mistake by staging a protest just before the Federal election.

More than 1,000 people attended a union rally at Parliament House last week, protesting against the government's education cuts.

Mr Barnett dismissed the protest at the time, calling it a Labor 'pre-election rally'.

In Parliament today he went further, accusing the union of being politically-aligned.

"The Teacher's union has a bit of a problem now," Mr Barnett said.

"They have engaged overtly in political activity, two days before a federal election by holding a joint protest with the Labor party and Mr Speaker there is no doubt about that; big, big mistake by the teachers union."

Mr Barnett also unveiled a number of winners and losers as part of the overhaul of the education sector.

He told Parliament that based on projected enrolments for next year, Mount Lawley and Balcatta Senior High Schools will each lose one teaching position.

Churchlands Senior High School will gain four teachers, while Ellenbrook Primary will get one additional teacher.