Lamb initially denied students had been breathalysed when contacted by the Herald on Sunday. Yesterday, however, he said the tests had taken place and thanked the Herald on Sunday for bringing it to his attention.
"Unfortunately, the deputy principal responsible for the breath testing was absent from school at the end of this week," Lamb said.
"The deputy principal reports that some students were tested, the majority simply curious about how the breath tester worked.
"One student, however, produced a low positive reading which was, apparently, residue from alcohol consumption the previous night.
"I will address the issue with the parents and student next week. The matter is now being investigated and the school will consider what consequences will be issued when the facts are known."
The school's senior students had their last full day of school on November 1 before going on study leave for NCEA examinations.
Traditionally, Year 13 students spend their final day at school in celebratory mode, often flouting school rules in end-of-year revelry.
Lamb said he was proud of how his school's senior students conducted themselves.
He said they finished the school year with dignity and decorum.
One high-profile student at the school is pop superstar Lorde.
Secondary Principals' Association president Tom Parsons said schools had a responsibility to provide a safe environment and anyone under the influence of alcohol posed a risk.
Breathalysers had been widely used for students attending school balls but it was the first time he had heard of it on the last day of term.
Deaker said: "Hopefully it will lead to people saying, 'Right, this is one thing that may assist', but the question is: why do young kids have to get drunk out of their brains to celebrate?
"I can't think of any problem in our country we have handled as badly as teenage drinking. When you consider the success we have had in changing attitudes towards smoking cigarettes, why haven't we been able to make the country's attitude towards teenage binge drinking more realistic?" He applauded any move to try to limit teenage alcohol consumption but said the problem also required attention from the highest levels.
"There are vested interests that are too powerful politically for any real progress to be made until somebody really has an agenda to make a change."
Takapuna Grammar PPTA chairwoman Ruth Blackman said the school had been happy with how the last day at school went.
PPTA secretary Dean Conger said the breathtesting was more of a "show and tell" thing.
Calls for harder line on drink-driving, Insight p12-13
