Chloe-lee Palmer spent part of the week co-ordinating ambushes and attacks on an unpopular classmate.
The rest of the week, she was scared to leave the classroom on her own, in case she was ambushed and beaten up in the corridor.
Fifteen-year-old Chloe-Lee is one of the leading actors in Wednesday's Child, a new film released into schools in early September.
The film, which is targeted specifically at schools, tells the story of Alison, a teenager victimised by bullies. The situation becomes increasingly heated when one of the pupils brings a gun into school.
David Chamberlain, writer and producer of the film, hoped to highlight the complexity and danger of everyday schoolyard bullying.
"I don't think there's any teenager who hasn't had experience of bullying," he said. "We wanted to show that there are significant misconceptions about who bullies are. People think that bullies are often big and male. But this isn't just a boy problem. Weapons come into play with girls as well."
And Chloe-Lee, who played the bully, found that her on-screen experiences were being re-enacted in her off-screen classroom. "I know what it feels like to be bullied," she said. "There was this one girl at school, and she turned the whole class against me. They were her puppies. No one would speak to me. They just followed her about. They'd knock over my chairs, come up in my face. It was horrible."
At its worst, Chloe-Lee was afraid to leave her own home, in case she was ambushed in the street. "I just wanted to bury myself in a hole and never come out," she said. "People don't understand what it feels like."
The aim of Wednesday's Child is to rectify this. Mr Chamberlain worked together with anti-bullying charity Red Balloon Society and a number of anti-bullying activists, to produce a teachers' guide to accompany the film.
"We don't profess to have the answers on dealing with bullying," he said. "But teachers and pupils can discuss ways in which they can help each other overcome problems around bullying. If we can change the lives of even one or two people, we'll have done our job."
Chloe-Lee, meanwhile, was able to use her real-life misery to further her filmic career. "Sometimes, in the role, I had to be really, really fierce," she said. "And I just thought of my bully. I saw what she was doing to me and thought, 'I'm just going to interpret it in the film.'
"No one's ever followed me about. I've never bossed anybody about before. But I wouldn't do that in real life. No way. I'm not that kind of person. Anybody who bullies someone is a waste of space."