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"If they don't work then the Government will close them down very quickly - if they do work then it will be great for the children involved," he said today.
He said the model had some success in the US, but he was firm they wouldn't continue here if they were failing children.
"If you look at the US where they are the most prevalent - there are about 5500. Not all of them are successful but many of them are," he said.
Education Minister Hekia Parata and Act MP John Banks announced further details on the "partnership schools" or kura hourua, this week.
Under the programme, unregistered teachers would be able teach classes.
Yesterday Mr Key said he wouldn't mind his children being taught by unregistered, untrained teachers.
Today he said technology teachers in the public education system were sometimes untrained and unregistered.
"Technology teachers have often been brought out of different disciplines and have gone and provided that support and learning for teaching for youngsters - so it's not unusual," he said.
Under the law unqualified teachers are entitled to teach under the "limited capacity to teach" category.
Mr Key said he would happily send his children to a charter school because they provided choice and flexibility.
Yesterday the Post Primary Teachers Association labelled the rebranding of the charter schools programme as "like putting lipstick on a pig".
"The unions will never agree. They don't agree in the US either. Both President Obama and Mitt Romney are on the record as being very supportive of charter schools in the US," Mr Key said.
"If you're waiting for the teacher unions to agree you will be waiting a very long time."
He said there was a high parental demand for charter schools in the US.
- By Kate Shuttleworth