The union for primary school teachers is frustrated at the decision to open seven new charter schools.

Up to seven new schools are to be funded, doubling the number currently operating.

Charter schools were introduced as part of Act's confidence and supply agreement with National.

Officially called "partnership" schools, they are privately run and publicly funded and set their own curriculum, school hours, holidays and pay rates.

But the NZEI's Paul Goulter says it would be better to fund education properly and get it working, with what's been proven to be effective.

Goulter insists that charter schools are a failed experiment.

"If you follow overseas evidence, there's actually no evidence that charter schools or similar - free schools, academies, or whatever - lift system performance," he said.

The NZEI also argue charter schools are small and funded for a guaranteed minimum roll, which is a luxury not afforded to public schools.