A Newshub investigation has discovered serious problems with the way some NZTA-approved contractors conduct testing for truck, bus, taxi and forklift drivers.
NZTA audited 150 providers in the last two years and found that 22 of them had "unsatisfactory audit results".
Several providers were helping students cheat - marking incorrect answers as correct.
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And in another case, students training to be truck drivers were given their practical assessments in campervans.
NZTA regulator Kate Styles believes some training agencies are deliberately cheating the system.
"There has been some of that behaviour and it has been deliberate and we are taking it extremely seriously," she told Newshub.
One audit found evidence suggesting the assessors themselves were writing answers in for trainees.
For those sitting Class 5 truck driving tests, it was noted "most questions are answered almost word for word as per the marking guide, indicating some assistance".
Another revealed "numerous instances of wrong, incomplete or inaccurate answers being accepted" as correct.
There was evidence of "poor records", apparently "lost" assessments, and one provider issued a course certificate before the course was even completed.
Last year Newshub revealed an NZTA-approved contractor in South Auckland was giving answers to students sitting taxi driving certificates.
That operator has now had its ability to do tests suspended.
There are 350 driver training organisations around the country. NZTA has audited 150 of them so far and 22 of those have failed, but only two have been shut down.
Master Drive is one of the country's longest established driver training companies and manager Neil Bretherton says he would "really happy to see more resources".
"At the end of the day we are training people to operate heavy vehicles and the safer they can be, the better," he says.
NZTA says where there's good evidence of wrongdoing it will take action. It now plans to introduce spot audits, where compliance teams can turn up unannounced to inspect the books.
Newshub.
