Wellington College has started an investigation after two students posted offensive comments on social media relating to rape and consent.
The two students described having sex with intoxicated, passed-out women in their posts to a closed Facebook group, with some of the comments "liked" by other students.
One of the comments, which were believed to have been posted on Sunday night, said: "If you don't take advantage of a drunk girl, you're not a true WC boy."
The comments were also seen by other students who were so concerned about them, they notified parents.
Wellington College principal Roger Moses said he was notified by a member of the public and the school was investigating.
He told Checkpoint with John Campbell the comments were deplorable and did not reflect the values of the school.
Mr Moses said the posts showed the dangers of immature boys on social media and should act as a warning to other school principals.
The school had spoken to the two boys involved and their parents, and the next step would be finding out when the comments were made and if they were posted during school hours.
The school was "obviously appalled and disgusted" by the comments, and the boys who made them were also "shattered" by what they had done, he said.
"I think the boys are absolutely distraught about what has happened. I don't, in any way, want to minimise what was said, but at times there is bravado that can happen on these websites, and I think that is probably what has happened."
He said the school could not control what was said in private groups online, and this was a real problem for schools.
"We can say the right messages in assemblies, we can have the right programmes in place, we can push the right values, but at times, regrettably, in the privacy of these chat rooms that we don't have access to, idiotic boys can say things that are very, very sad, and that's what's happened on this occasion."
He said there was a danger of a moral corrosion amongst young people, who needed to understand that such comments were not just a temporary thing.
"It's been said, and it can't be unsaid."