Principals say they are being hamstrung by new search and seizure rules allowing them to look in a student's bag but not search it.
With the new rules set to start as schools go back next week, principals say they do little to guarantee student safety.
The reality for schools is that weapons, including knives and screwdrivers, are being brought on to school grounds and the new guidelines limit the extent to which searches can be carried out.
Teachers can look inside bags, but not search for buried contraband, and if dangerous equipment such as scalpels go missing a class cannot be searched.
Seized electronics in suspected cyber-bullying cases can also not be checked for content.
Former Secondary Principals' Association president Patrick Walsh said schools had been back and forth to the Ministry of Education 10 times in an effort to redraft the rules, but some principals would remain unhappy when the guidelines came into force.
The ministry said the legislation had come into effect on January 1 and the guidelines for principals would be signed off next week.
Association president Tom Parsons said it would be terrible if after 10 redrafts the guidelines were not workable.
"When you seize a phone and trawl through it you may see stuff that is arguably private, but that's nonsense to then not do it, because the reason you're looking for the stuff is out of good intentions."
He said principals and teachers did not use search and seizure powers unless there was a reason to suspect wrongdoing. "Surely the privacy factor is a small price to pay for the greater safety of all students."
Children's Commissioner Russell Wills said those at the coalface of teaching needed to be writing the guidelines, but they could only explain the law, not change it.
- Fairfax Media
Have you had a ticket in the last five years?Related story: Canterbury speed camera use rises sharply