"Our community is very supportive of what we do."
McKinley said he would be surprised if other schools didn't use pat-down searches at their balls.
ACG Parnell College has informed parents of plans to use a sniffer dog and testing agency, to check students for drugs and alcohol, at its school ball in July.
The Ministry of Education deputy secretary sector enablement and support Katrina Casey said current search and surrender guidelines "state clearly that patting down is not allowed".
"Visual assessment at entry of students' condition and behaviour may occur and entry can be refused based on a judgement about a student's condition.
"A search does not need to take place before arriving at that decision."
Casey said the Ministry's responsibility was to ensure school leaders were aware of the guidelines and did not expose themselves to a legal battle.
The Ministry's guidelines stated outside venues may have their own rules around entry to a function on their premises however, "schools are not permitted to conduct a search that involves searching a student's person/body".
A spokeswoman for the Pullman Hotel told the Weekend Herald the venue does not enforce pat-down searches in their ball contract with schools.
McKinley said staff from the Pullman Hotel would conduct the pat down, not staff from the school.
He said he would relook at the school's contract with the Pullman Hotel but as far as he was aware, the school was entitled to have security guards pat down students.
When students arrive at the ball, they form two cues - males on one side and females on the other - so they can be pat down by "professionals" of the same gender.
Any students who fail any safety or security checks throughout the evening would be asked to have a parent or caregiver collect them, according to the letter.
New Zealand Council of Civil Liberties' spokesman Thomas Beagle said patting down students seemed "over the top".
"One question we want to ask is 'would we accept schools having pat down searches at the school gate each day' and I think the answer to that is, that would be obviously ludicrous and wouldn't be acceptable.
"It's a state institution doing an unwarranted and untargeted search.
"To my mind, you have to have some really strong reason to justify even looking at such measures."
Beagle said Kiwis are protected from unreasonable search under the Bill of Rights Act.
Secondary Principals' Association (SPANZ) president Michael Williams said he was aware that schools cannot conduct random or invasive searches of students however, the ability for a venue to require pat downs was a "bit of a loophole".
"The thing that is paramount here from the school's perspective is to ensure the students are safe.
"[SPANZ] applaud principals who take their job seriously and ensure the safety of their students but we also assure that our members adhere to the legal requirements around search and seizure."
