Giving fingerprints or DNA samples may be the only way to ensure that convicted sex offenders cannot simply give a false name and then be approved as a teacher, says the head of the Teachers Council, Peter Lind.
But he said that such a move would be controversial - but it needed to be part of the discussion. Mr Lind admitted that the council relied on applicants to tell the truth.
"We have checks and balances, but is it 100 per cent foolproof? No.
"It's only really through a live ID like a fingerprint, or a DNA [sample] - we've got 98,000 teachers out there and every year there are 28,000 re-registering. ... [It would] cost a lot."
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Meanwhile, parents are upset at the level of support provided and that they were not fully informed from the outset; a letter from the school did not say he was convicted of a sexual offence.
Education Minister Hekia Parata said the Education Ministry's trauma incident team was available to schools from Tuesday, and on the ground at those schools yesterday.
But the parent said that efforts to seek help went unanswered.
"My expectation is that the ministry would be flooding those schools, the parents, the principal and the board of trustees with the support that was needed, and that that support was there on Tuesday morning."
Mr Lind said the council had since checked the teachers' register for other possible cases and was pretty confident "we are unlikely to see another case".