A key figure involved in setting up the Novopay service says the Education Ministry rushed out the system because it was desperate to meet self-imposed deadlines.
School Payroll Reference Group adviser and Baradene College principal Sandy Pasley said the rushed decision saw mistakes occur before the error-ridden payroll even launched.
She also said Talent2, the firm that designed Novopay, completely misjudged the complexities of the project and the ministry relied on that flawed judgment. The reference group was assembled in 2008 to give feedback to the ministry on Novopay.
However, advisers could not make decisions.
Pasley said Novopay was meant to roll out in stages so problems could be identified early and fixed.
"Right up to last year there was going to be a staged rollout and we talked about trialling Novopay," she said. "It should have been trialled on a smaller basis first. But it got to the stage where it was so complex to put together and the deadline was looming."
Instead, it was pushed out nationwide in August - leading to countless mistakes, with more than 8000 logged errors in teachers' pay.
Some staff have not been paid since the launch.
A breach of security revealed last week in the Sunday Star-Times meant staff at Auckland school Marshall Laing Primary were given access to hundreds of teachers' banks accounts and personal details.
Pasley said a rollout as planned could have limited this kind of problem.
"I'm really disappointed that it couldn't have been trialled with a much, much smaller population first. Some of these problems might have surfaced and been ironed out before it went nationwide."
Education Ministry group manager Rebecca Elvy admitted the original intent was to roll Novopay out in stages. The South Island should have received the service in 2010 and the North Island in 2011.
"This was an agreed decision by the ministry and Talent2," she said.
But "time pressures made a staged rollout not feasible" and it was decided all schools would go live on the same date, August 20 this year.
Pasley said the delay could be blamed on Talent2 not realising the intricacy of the project.
"Maybe Talent2 misjudged the complexities of the New Zealand payroll system," she said.
"I think the Ministry of Education relied on Talent2 to deliver, so have the whole sector."
The ministry has stood by claims Novopay was "rigorously tested" prior to its implementation.
"In addition to the continuous testing of system features as they were developed, there were two full simulations and six cycles of payroll verification before go live," Elvy said.
However, Pasley is not convinced the ministry and Talent2 did enough.
Elvy would not comment on what accuracy the ministry required from Talent2, nor what accuracy it was currently performing at.
"The answer to both of these questions is commercial and in confidence. We cannot disclose this without breaching our terms of the contract," she said.