Testing of Novopay call centres revealed a 50 per cent error rate - even before the troubled system went live.
Documents show that in a 'mystery shopper' audit of the service centre, half the phone calls made to it were answered incorrectly. Half the paperwork submitted to it also contained errors.
The testing was carried out over five days in early August. The system went live later that month and since September thousands of staff have been over or under paid.
Among the problems identified were staff providing incorrect advice and issues with a 'web chat service'.
Labour's acting education spokesman Chris Hipkins said the government should never have let the system go live, knowing it was not "up to the job".
Hipkins said wait times for the call centres ranged from 10 to 29 minutes.
"That’s huge waste of time and money for schools."
“The Government and Talent2 created this mess. The very least they can do is help schools clean up after them,” he said.
Novopay minister Steven Joyce has launched a ministerial inquiry and diverted extra resources to get Novopay functioning - but he has warned there won't be a quick fix.
But the Post Primary Teachers Association said school staff were "buckling under the pressure" of the broken system.
The union wanted a "rescue package" in place, which included more staff in the call centres.
President Angela Roberts has written to Joyce and acting education secretary Peter Hughes asking for financial compensation, extra support-staff time, and a a one-off special leave provision for principals working overtime on Novopay problems.
Each school should also get a an identified contact person in the call centres.
President Angela Roberts said it was "unacceptable" resources were being drained from schools.