Questions have been raised whether the trial will have the best accountability structure; the National-Act confidence and supply document says schools will answer to sponsors and be subject to review.
But Ms Davis said charter schools in the US that were performing well were accountable to the state. She pointed to a law in Indiana, passed this year, that provided clear goals for charter schools and effectively gave the state a veto power on poor performing providers.
"If the school hasn't met the metrics that were agreed upon, they get shut down. The state sets the parameters and the school sponsor or authoriser is charged with carrying that out."
A Credo study in 2009 of charter schools in 16 American states found almost half of the schools were no better than public schools; 17 per cent performed significantly better, while 37 per cent performed worse.
"No one has found a magic bullet that will make sure all kids learn and are ready to go to university. It doesn't exist. It's just one tool in an arsenal and it has to be used correctly," Ms Davis said.
Act MP John Banks, who will be Associate Education Minister responsible for the trial, declined to answer questions on accountability measures and whether the trial would require a law change.
He said he needed to talk to the incoming Education Minister.
The New Zealand model will be based on programmes such as the US Knowledge is Power Programme, which has been lauded for good results in maths and reading.
A report this year found one third of students who completed a KIPP at least 10 years ago have a university degree today, compared with 8 per cent of similar students.
But a 2005 report by the US-based Economic Policy Institute said KIPP had good results because it selected motivated students. The institute found no evidence that the average charter school performed better than a public school. It found greater freedom from state regulation produced some excellent schools but also some poorly managed and even corrupt ones.
HOW THEY WORK
* School boards are free to operate schools as they want or contract management to the private sector.
* Schools have more freedom to set curriculum, length of the school day, performance-pay for teachers and raise revenues through sponsorship.
* Public funding to continue based on student numbers. No tuition fees.
* All students are accepted regardless of ability. If over capacity, a ballot system can be run.
* Providers compete to run existing schools or set up new ones.
