The device, introduced this term, is used when a pupil parks a vehicle which he has failed to register with the school, on its grounds. Pupils wishing to park vehicles on school grounds also have to sign a contract which outlines acceptable behaviour.
A vehicle is also clamped if a pupil fails to abide by the conditions of the contract, which include obeying road rules.
A vehicle would remain clamped until the pupil paid a $25 "unclamping" fee.
Rector Paul Jackson said he had used a clamp at his previous school, Marlborough Boys' High School, after seeing the method used successfully in some Australian schools.
He and his staff had a "moral responsibility" to protect pupils and the initiative was instituted to prevent them from "taking the law into their own hands".
A pupil having a vehicle accident on the way to or from school, or at lunchtime, was a rector's worst nightmare, and, in that circumstance, having a record of each vehicle would be of great benefit, he said.
Early in the term, the clamp had been in Mr Mattisson's office window as a deterrent. The tactic worked, with 51 cars registered within a matter of days.
Mr Mattisson said vehicles parked outside school grounds were exempt. The scheme made it easier for the school to identify the owner of each vehicle and, as a result, how each vehicle was legally allowed to be used.
The threat had worked so well the clamp had still not been employed.
"It's in pristine condition at this stage," Mr Madison said.