Secretary for Education Lesley Longstone has admitted she would have rolled out the Novopay school payroll system differently if she could turn back the clock.
"If I were to do it again, I would probably do it completely and totally differently," she told the education and science select committee today.
The problematic Novopay school payroll system will be independently reviewed after ongoing errors in paying school staff.
The review has been called for after Talent2 and the Ministry of Education rolled out the payroll system in August.
Ms Longstone said the review would look at the roles of the ministry and Talent2 in the administration of the system.
Asked if the review was a bad look, Minister in charge of Novopay Craig Foss said: "the performance of Novopay early on was a bad look."
The review would be carried out next year and would look at why there were problems with Novopay when it went live, why Talent2 and the ministry weren't ready for them and what could be done differently.
Ms Longstone was questioned by opposition MPs about why Novopay was not trialled before it was rolled out.
She said the system was one of the most complex in Australasia.
"Trialling it in some schools would have been practically impossible, because of the fact so many teachers work in a multiple number of schools and move during the year between one school and another."
"Trialling it in a particular areas means that you'd have people on two systems simultaneously and it was just not possible."
Ms Longstone said the payment mechanism of Novopay was tested by running entire payrolls through both the previous system and Novopay and got the same outcomes.
She said software that input payroll information had suffered problems.
"The bit of the system that produces the reports back out to schools had had bugs as well - where we've had real difficulties is with the two user interfaces at the input and output side."
There had been a back log of 8000 errors with Novopay - but most had been cleared.
Ms Longstone blamed staff collective agreements for some of the outstanding problems, which were created by staff being paid under 13 different agreements, within each of those different pay ranges and up to 400 different pay arrangements.
Ms Longstone said there were up to 10,000 different pay combinations for paying staff in schools.
She said there were things to learn from the rollout of Novopay.
Ms Foss said the number of issues resulting from the payroll transition had been unacceptable.
"There are several key milestones coming up including end-of-year and start-of-year payments, it is important they are captured by the review.
"It's also important that the review does not detract from the immediate focus of getting the payroll system running to its full potential. Right now the focus is on getting school staff paid accurately and on time," he said.