Principals say they are being hamstrung by new search and seizure rules allowing them to look in a student's bag but not to search it.
With the rules set to kick in as schools restart for the year, 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 but the guidelines still do not ensure such items will be found, because the 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 goes missing, a class cannot be searched.
Electronics seized in suspected cyber-bullying cases could 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 with them.
The ministry said the legislation came into force on January 1 and the guidelines for principals would be signed off in the 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."
Parsons said there was no point getting "tied up in the detail" and principals needed to exercise their right to keep students safe regardless of what the guidelines said.
Walsh, principal of Rotorua's John Paul College, said the biggest difficulty was finding a balance between students' privacy and safety within a school.
He planned to approach Education Minister Hekia Parata to discuss what more could be done to increase safety.
Parata said she would consider looking at further improvements once the guidelines had been in place for a while.
The guidelines had addressed some of the main concerns and some teachers would be happy with them, Mr Walsh said.
"But for others there has to be a balance in protecting students' rights and making the school a safe environment."
Cyber-bullying, where students share inappropriate pictures and messages and post them in public forums, is an increasing problem in schools. A committee is being set up next month to specifically tackle guidelines for principals on managing cyber-bullying and giving teachers the power to confiscate and delete inappropriate material.
Walsh said the information he received from schools through a survey last November was that recording sexual assaults and behaviour and bringing it to school was more widespread than thought.
He said suicide had been strongly linked with cyber-bullying and eliminating it in schools was high on the agenda.
At Rongotai College common sense was the over-riding factor in searching students, principal Kevin Carter said. "If you're concerned for a child's safety you'll do something about it. Common sense would always be the driver."
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.
Teachers are allowed to ask to see inside a student's bag but not openly search through it for particular items.
If a dangerous scalpel goes missing from a science lab, individual students can be asked if they have taken it but the entire class cannot be searched.
If an inappropriate recording has been taken on a mobile phone in a changing room, the device can be confiscated but a teacher can't look through the phone or delete the footage.
- The Dominion Post