Secondary principals say knives are the most common weapons brought into schools by pupils - either for bravado or self defence.
Mr Kersten said weapons and drugs were not an issue for his school. The new guidelines were necessary for student safety and reflected search procedures staff already practised, he said.
"Anything that enables us to do that better with less hassle and greater authority ... the students and the school community will be better off for it."
Secondary Principals' Association ex-president Patrick Walsh said education representatives were meeting with the Education Ministry this week to discuss how the rules would affect electronic devices, which could be used for cyber bullying.
At present teachers could confiscate tablets or smartphones, but could not search the contents.
Schools had a small window of opportunity to delete malicious or intimate images of students, before images were uploaded to the internet by an offending student.
Mr Walsh was keen to see the ministry work with internet providers and internet safety body NetSafe to improve students' safety from cyber bullying.
Current association president Tom Parsons said although some principals would not be happy with the new search rules and guidelines, the legislation gave schools clarity on what they were legally permitted to do.
"The effectiveness of these [rules] will come out in the fullness of time."
Some principals had to search students on an almost daily basis, whereas others only needed to do so occasionally, so it was difficult to issue a "blanket guideline".
Knives were the most common weapon Kiwi students brought to school.
"Kids mistakenly think that they're going to be better protected by carrying a knife."APNZ