Teacher union slams charter schools

National is committing political suicide by agreeing to set up charter schools, a teacher union says.

The post-primary teachers union (PPTA) says they've been "a disastrous experiment" overseas and the government hasn't even reviewed the evidence.

Establishing the schools is part of the support agreement signed on Monday by Prime Minister John Key and ACT's sole MP John Banks.

"There doesn't appear to have been any assessment of the venture's cost or the value of its return either," PPTA president Robin Duff said on Wednesday.

"For National to incorporate another party's such poorly-concocted education policy into its own education portfolio looks like political suicide - the party should know better."

Mr Duff says there's been a partnership between state schools and industry for years, giving students skills to move into the workforce.

That's one of the results Mr Banks expects from charter schools, which will be run by private enterprise, iwi or community groups outside the rules that govern state schools.

The Greens are challenging the government to say where the money for the schools will come from.

The agreement says public funding will be provided and education spokeswoman Catherine Delahunty suspects existing state schools will suffer cuts.

"National and ACT's agreement to set up and fund this form of private school is a huge policy to spring on the electorate post-election," she said.

"The government must explain if new spending has been allocated for this project or if the spending will come from existing education baselines."

Ms Delahunty says state schools in the poor areas chosen for the first charter schools need every cent they get to meet the needs of their students.

"If this policy is to be paid from the already stretched education budget then presumably cuts will have to be made that will affect those schools that are already struggling."