The Prime Minister says he's open to the idea of state schools being converted under a partnership school model, a move being pushed by ACT Party leader David Seymour.

Currently there is no policy that allows such a move, but Mr Seymour says he's keen to negotiate if he's in a position to help form the next Government.

"In New Zealand politics you have an election every three years so you have to break things into chunks. In this chunk we are making sure that we have a successful partnership model, I think we've made a lot of progress at that. And then the next chunk I guess will be to say, 'how can we help more kids through this policy?'

"Maybe in a year's time I'll be in a position to negotiate that with a fourth term Prime Minister John Key and we'll keep going forward growing this policy," he said.

And Mr Key says he wouldn't rule the idea out.

"We would also accept that there are some state schools that are failing and there's some change there and some intervention would be useful so I'm not ruling it out.

Mr Key says the Government hasn't delved further into the issue and agrees any move to address it would be done after the next election.

"Whether we would move to a step where they would actually take over a school that's in the state system that's failed is a very different matter and we haven't really gone and done any analysis of that or given much consideration whether it could work. We certainly just haven't ruled it out," he said.

The latest addition to the charter school line-up was announced on Tuesday which will make a total of 10 schools nationwide.

But Mr Seymour says he's been approached by state schools interested in switching to the partnership school model.

"There's no government policy for state schools to turn into partnership schools but I know that there are people out there who operate state schools who have actually said to me they would actually be quite interested in making a conversion."

Teacher union NZEI has been quick to criticise the move as further privatisation of the education system.

NZEI's Lynda Stuart says the move would be ludicrous.

"He's using a position in Parliament to try and push his own agenda of privatisation of our schools and the only thing that I can think of is that it’s all around money," she said.

Ms Stuart says any state school looking to convert under the partnership model would no doubt be enticed by the financial benefits.

"I sort of think why would you do that for a start unless you thought you were going to get more money and if that’s the case, is that about the children?"

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