An Auckland school has banned its final-year students from attending their last full day of classes tomorrow in a bid to avoid pranks.

Mt Albert Grammar School, one of the country's largest schools with 458 Year 13 students last year, held a special Year 13 assembly this morning to tell students not to come to school tomorrow.

Headmaster Patrick Drumm said he did not want any "silly stuff" from students, and said security would be beefed up.

Student Ryan Naran said the announcement surprised both the students and their teachers, who traditionally planned "a bunch of fun events and shared lunches" for the final day of school before students go on study break.

"We all chip in and get them a gift. It's just a nice day," he said.

But the tradition also included "pranks" such as water fights and boys and girls swapping uniforms for the day.

"He made it sound like he was giving everyone an extra day of studying, but he definitely said it was about avoiding pranks," Ryan said.

"He said he trusts us like adults, but then he made it clear that he doesn't trust us at all."

Ryan, who has been at the school for five years, said he was "really upset" by the decision.

"It just doesn't feel like a fulfilling end," he said. "The entire year group is outraged by this."

Drumm confirmed that he made the decision partly because many staff would be involved in the Year 11 prizegiving tomorrow, but also partly to prevent "silly stuff".

"Yes, it's also to send a pretty strong message that it's business as usual, and while it's a special day for the Year 11s, we don't need any of this silly stuff that can creep in at this time of the year," he said.

"We don't tend to get the wholesale pranks, we don't get wholesale behaviour like that, but yes, we have had other students from outside the school come and make a point and leave their mark or whatever you want to call it.

"And yes, like most schools, we will be looking at some sort of additional security. Security are involved in the school all the time. We are involving them a bit more at this time of the year to keep the school safe."

However he said the extra security would only be at night.

"We won't be having security during the day," he said.

He said some Year 13 students would be involved in the Year 11 prizegiving, for example to support siblings in Year 11, and others would need to come to school to sort out arrangements for the National Certificate of Educational Achievement (NCEA) exams which begin on November 7.

Associate principal Jo Williams told parents in an email that if Year 13 students need to see the NZ Qualifications Authority representative tomorrow, "they are to come to school in uniform and register ... that they have come in temporarily".

Drumm said Year 13 students would also be back at school on Monday for their own prizegiving.

But another Year 13 student, Theo Heeringa, told Williams in an email response that many students would not be there on Monday.

"There are many people I know who will not being attending school on Monday and It pains me to think that I am not going to be able to say goodbye to them," he wrote.

"I was looking forward to savouring the last normal school day, not only with my friends but with the staff who have given me so much support over the years.

"It feels as if I have been robbed of a milestone in my life, I will never have a last day of high school."