Some charter schools are enrolling difficult students and having trouble attracting good teachers, the Education Ministry has been told.
A ministry report found some newly established charter schools did not do well last year, though it was too early to draw conclusions.
The report said the four remaining charter schools from the five set up in 2014 performed well last year, but the four new schools that opened their doors in 2015 generally did less well.
It said it was too early to draw definitive conclusions about the progress of the new schools and mentioned factors that might have contributed to their results.
"In the case of three of the four Round Two schools, students enrolled throughout the year, meaning that the school had less than a year to get them to the required standard. In some cases, the new students were well behind on joining, making the task even harder," the report said.
"Other reported factors impacting on progress are difficulties in attracting quality teachers, student transience, the high rate of referrals from Child Youth and Family and the Police and referrals of difficult students from other schools."
All of the organisations that ran charter schools said their students had histories of disengagement from school, according to the report.
It said the ministry was trusting the schools' owners to accurately report their performance against the performance measures in their contracts.
"The ministry has generally accepted the information provided by these sponsors in the annual reports," it said.
"The ministry has no external information to suggest that the performance reporting in the annual reports is inaccurate such that it would have warranted an audit or other information-gathering."
The report said the ministry must also accept the schools' internal assessments of students' performance against the national standards in reading, writing and maths.
"We have done reasonableness checks and have found no reason to question the reported data."
The report said the schools' owners had asked for changes to performance measures related to student attendance and discipline, because they could exceed those measures due to disciplinary action with a very small number of students.
"They also argue that these standards could result in a school not taking the appropriate disciplinary action in order to ensure that it achieves its performance standard," the report said.
The report said five of the eight schools did not meet their guaranteed minimum roll for which they were funded last year.
Another ministry document showed the government had allowed four of the schools to offer religious instruction this year because it was consistent with their special character.
The schools were South Auckland Middle School, West Auckland Middle School, Pacific Advance Senior School and the Rise Up Academy.