Charter school students outperform their public school peers in some areas, a new study shows, as the Government continues to work towards introducing the controversial schools in New Zealand.
However, New Zealand's largest education union says the United States research shows improvements are far from those promised, some 20 years after the first charter schools opened there.
The study by Stanford University researchers at the Center for Research on Education Outcomes examined the standardised test results of students enrolled in charter schools in 26 states and New York City.
Results were compared to those of students with the same demographics and academic profiles in public schools that the charter students would have otherwise attended.
The original study in 2009 found many students in charter schools were not performing as well as those in nearby public schools, and was widely cited by opponents of the publicly funded, privately-run schools.
However, the updated study shows that, overall, charter school students are now surpassing those in public schools in reading gains and keeping pace in maths.
Education Minister Hekia Parata will confirm the operators of the first schools, which will be publicly funded but privately operated, by August, with up to five set to open in 2014.
The Government has downplayed comparisons to overseas models. Last week Education Minister Hekia Parata signalled she would not answer questions at the education and science committee unless members referred to charter schools as partnership schools.
And yesterday a spokeswoman for Act Party leader John Banks, the minister responsible for partnership schools, said the US study was not directly relevant to New Zealand.
"It is always good to see schools improving outcomes for their students, but it must be remembered that the Partnership School model is unique to New Zealand," she said in a statement.
The Stanford study found the average charter school student showed gains in reading equivalent to those expected from an extra eight days of learning compared to traditional school students, with improvements in maths about equal.
The 2009 study found charter students lost the equivalent of seven days of learning in reading and 22 days in maths.
The improvement was helped by the closure of 8 per cent of schools included in the 2009 analysis because they were underperforming.
New Zealand Educational Institute president Judith Nowotarski said the research showed that despite the grand promises that surrounded charter schools, their success in raising performance was negligible.
"I don't think it gives any great evidence that charter schools in the States have made the gains they said they'd make. In fact, they should be disappointed that it has taken so long to record any point of difference."
Ms Nowotarski said the union would be keeping close watch on the Government's announcement of who would be allowed to operate schools here.
"We will be seeing who is setting them up, the promises they are making, and if they are going to deliver."
# United States study of charter school students in 26 states compared results to similar students at neighbourhood public schools
# Average student gains an additional eight days of learning each year in reading beyond their peers in traditional public schools
# No significant difference in mathematics
Source: National Charter School Study 2013, Stanford University's Center for Research on Education Outcomes