St Hildas Collegiate has stood down more pupils in one day than most secondary schools stand down in an entire year.
Eighteen pupils were stood down for two to three days last week after they were caught with alcohol at their school formal in the Dunedin Town Hall on May 16.
Principal Melissa Bell said the incident had left her disappointed.
"We have a zero tolerance policy for alcohol at school events.
I think we are being firm and consistent, and we are sending a very clear message to the community about our expectations for our pupils."
Ms Bell said the school provided written documentation to all pupils outlining the school's expectations for behaviour at the formal and a special assembly was held before the event to reiterate the information in the document.
All pupils had signed a contract saying they agreed to the terms, before being given permission to attend.
The 18 pupils (aged 15-17) were caught with concealed hip-flasks by security staff at the formal, although none of them was intoxicated.
Ms Bell believed they were carrying the flasks for consumption at functions after the formal.
Once pupils left school functions, she said, it was impossible to prevent them from drinking alcohol because they were the responsibility of their parents again.
Despite the incident, Ms Bell said the majority of the 300 pupils at the function were following school policy and had a wonderful evening.
"Most of the girls that had alcohol came forward and accepted responsibility. I'm proud of them for doing that.
"I'm sure they will learn from the mistakes they have made. Parents and the community are very supportive about the clear stance we've taken."
All 18 girls were now back at school after individual meetings with the principal to make sure they were aware of the gravity of what they had done.
A review of the way St Hildas Collegiate ran school formals was in progress and an alcohol education seminar with "outside experts" would be held later this year for the pupils involved, Ms Bell said.
The Otago-Southland Secondary Principals Association chairman and John McGlashan principal, Mike Corkery, said it was an incident which happened at the best of schools across the country.
"Kids do silly things and we have to deal with it. What else can you do?"
But he questioned the role of school formals in the lives of today's pupils. "At one time, it was an opportunity to dance. For many kids it's just a warm-up for a big party now.
"It makes you wonder why schools are in the business of running formals - especially when some kind of after-match function is the norm.
"We all know it goes on and we don't agree with it."
