"It is not possible for students to be picked up from the venue or for them not to return on the bus," the school newsletter said.
The tough line follows several years of controversy over school balls and after-parties including concerns about pupils becoming extremely drunk and taking drugs.
Other schools are also making big changes, including one which brought in police to warn students what would happen if they were organising an afterball party.
Diocesan School for Girls advised parents and students not to hold events after the function, and asked them to keep the ball, which was held on Saturday, as the "main event".
The Epsom school employed a security company with drug dogs to watch over the students as they arrived and to check for anyone who had been drinking.
A parent of a girl at the school said that after teaching staff were told of plans for a party, a police liaison officer told the students at an assembly that afterballs were illegal.
Principal Heather McRae refused to say whether anyone was denied entry or was asked to leave during the ball, but said the event went well and everyone had fun.
Baradene College, which held its ball last month, also went to great lengths to ensure there were no after-ball parties.
Parents picked up students from the door of the ball venue, the Viaduct Events Centre in Wynyard Quarter.
"And as far as I'm aware, there weren't any afterballs," principal Sandy Pasley said.
A teenage boy who was a guest of a student at the girls' school, was not allowed into the ball because he was drunk.
He sat with teachers until the event ended because his mother was unable to come for him, Mrs Pasley said. That had been the only incident of note.
Senior students at Westlake Girls High School are preparing for their school balls, one for Year 12 pupils this week, to be followed by the Year 13 ball.
Principal Roz Mexted said the school had sent out newsletters reminding parents that the school did not condone any functions after the ball.
"We have spoken to the Year 12 students... We talked about the importance of making wise decisions and about looking after themselves.
"We've got a letter that we will send out to parents... we've seen schools suffer enormous losses and we want the parents to be right there on the same page as us. The ball is a well-organised school event and that should be it."
King's College will be not holding a ball this year following the death of student David Gaynor after last year's function.
Some schools have chosen to organise their own after-ball functions to combat students continuing to party without supervision.
Kristin School will be holding its ball at the start of next month at The Edge and has organised an official afterball at the same venue.
Principal Peter Clague said the school did the same thing last year because "if it was going to happen anyway, it's better to do it under our watch".
Not every parent thinks afterballs should be banned. The mother of a Diocesan pupil said she and her daughter tried unsuccessfully to persuade the school to let them organise a function.
"It just makes no sense. I'm quite strict and I would feel much more comfortable with my daughter going to a professionally-run afterball with supervision and security, otherwise these girls are going to get on the streets doing God knows what," she said.
Glendowie College, which had had its ball at the weekend, organised a professionally run afterball party.
Director Cade Pellett said the event was successful, but up to three people arrived intoxicated and were asked to wait outside in a "chillout area" for an hour while drinking water before they were allowed in.
