A review of the Government's controversial charter schools experiment will not compare the performance of the new schools' students with comparable students in state schools.
The first comprehensive evaluation of charter or "partnership" schools will help determine whether the privately run, publicly funded model expands.
But a teacher union has dismissed it as worthless and the Act Party - which introduced charter schools as part of the party's confidence and supply agreement with National - has asked for the review to be beefed up just days after it was outlined.
Several of the nine charter schools are performing strongly, but Te Kura Hourua ki Whangaruru in Northland is close to closure after ongoing problems and a falling roll.
An evaluation plan released this week outlines how the partnership model will be evaluated. MartinJenkins, an independent and respected education consultancy, will carry out the work, which will run until November 2017.
The Ministry of Education has defended the process after it was slammed as worthless by the Post Primary Teachers' Association (PPTA).
Union president Angela Roberts said that high-quality charter-school evaluations overseas had compared the achievement of students in charter schools with how they would have been expected to perform had they stayed in public schools.
The MartinJenkins plan states that, "ideally, we would assess impact (i.e. the extent to which outcomes are attributable to the policy) through an experimental or quasi-experimental approach".
However, it rules a comparison of charter school students' results to comparable state-school students "is not desirable at the school level or possible at the student level, due to a lack of access to data regarding non-partnership school students and their outcomes".
Ms Roberts said the budget of $375,000 was not adequate for a comprehensive evaluation.
"This Government prides itself on evidence-based policy that works ... they are getting what they are paying for - a cheap and shoddy exercise."
It was also disappointing that charter schools' impact on surrounding schools was not included, Ms Roberts said.
Act leader David Seymour also said he had hoped for a more in-depth approach, and had requested a meeting with MartinJenkins.
"It is my intention that in the fullness of time there will be a statistically robust, quantitative comparison of the performance of partnership schools kura hourua vis-a-vis comparable students in comparable state schools.
"Our basic commitment is that we are doing a pilot model and, as such, we should actually do an apples-to-apples comparison of how they have performed.
"I wouldn't say I'm unhappy with the evaluation plan as it stands.
"They have done a lot of work there, but I have asked to meet with them to challenge them on the idea that it is not possible or desirable to do a quantitative comparison."
A spokesman for Education Minister Hekia Parata referred questions to the Ministry of Education, as did MartinJenkins.
Dr Graham Stoop, the ministry's head of student achievement, said the evaluation "will tell us what we need to know about the model to assess whether it is achieving its objectives".
Meanwhile, an audit led by Deloitte is under way at Te Kura Hourua ki Whangaruru, also known as Te Pumanawa O Te Wairua, at a cost of $50,000 and will influence Ms Parata's decision on whether to close the school.
The test for charter schools
•An outline of how the charter or "partnership" school model will be assessed has been released by the Ministry of Education.
• The work will be completed in 2017 and presented to the Cabinet, helping inform a decision on whether the controversial school model will expand.
• Act leader David Seymour has requested a meeting with consultancy Martin Jenkins, asking them to reconsider part of their approach. The PPTA has been more critical, labelling the planned evaluation worthless.