A website set up for pupils to share their experiences of sexual harassment during their time at a grammar school has received more than 140 testimonies.
The Kegs Survivors website was created as a "safe space" for former and current students at King Edward VI Grammar School in Chelmsford, Essex.
Former pupil Imogen Greenwood, 21, who helped set it up, said stories of "sexism and misogyny" were shared.
The school said it was "extremely saddened and horrified" by the posts.
King Edward VI Grammar School, known as Kegs, is a selective state all-boys school up to GCSE level, that takes on female pupils in the sixth form.
Ms Greenwood, who left the school in 2018, said the incidents reported on the website happened at "house parties, outside of school and inside of school".
The Leeds University student said while most of the testimonies were about sixth form pupils there were also reports of younger boys behaving in a "predatory nature".
On the website, one person wrote of the "lack of respect these boys have for women" after she was "harassed" at a party with "Kegs boys".
Another told of when she rejected one boy, he and two of his friends "set out to make my life miserable, and they succeeded".
Men have also posted sharing their experiences with one apologising "to all those who I may have hurt during my time at the school", while others have written about being the victims of sexual assault.
Fellow former pupil Kezia Mbonye, also behind Kegs Survivors, said it was when she saw the Everyone's Invited website - which offers a similar platform - that she became "empowered to speak up".
The 20-year-old, now at Durham University, said the experiences shared went back 10 years.
In an open letter, the school has been asked to reform sex education, have "a rigid zero-tolerance policy" for misogyny, sexism, harassment, abuse, and assault, and to hire specially-trained members of staff to help victims.
It also called for "safe spaces to talk about sex and relationships".
Thomas Carter, the school's head teacher, said: "It is totally unacceptable that misogyny, harassment and abuse in any form take place - and it is also not sufficient for anyone to be a bystander on these issues."
He said the school was involving current and former pupils as well as parents and staff in process "to change these appalling attitudes".
"We would encourage anyone who believes that they have been the victim of a criminal act to go to the police if they have not already done so," he added.