A Christchurch school says it may be criticised for serving alcohol to under 18-year-olds at its school ball.

Christ's College holds its $175 a head annual school ball next Friday, complete with three-course meal and a full bar, The Press reported.

Headmaster Simon Leese said parents had given written permission for their children to drink alcohol at the event.

He said parents realised that their sons and daughters would be in an unsupervised tertiary environment next year.

"The easiest position for a school to take is to have a no-alcohol policy."

However, this had been shown to have no impact on the prevailing youth-drinking culture, Mr Leese said.

He said the school was addressing the "youth drinking" problem responsibly.

Pupils were not allowed to drive to or from the ball and everyone had to agree not to attend after-parties.

Alcohol Advisory Council (ALAC) chief executive Gerard Vaughan said schools could make their own call on balls.