After she upset a fellow student with a posting she says was "meant as a joke", her mother banned her from using the site.
"I tell everyone my new name and get loads of friends as soon as," says Harriet. "My mum is on Facebook and she'd see if my name was up. I don't do it on our computer at home, only at ICT in school and on my iPhone.
"It's not as good on the iPhone for seeing pictures, but you can use it late at night in bed. You can't not be on it, or you just don't have friends."
Concerns over children setting up Facebook accounts and lying about their age are not new. Facebook's terms and conditions, which were put in place to comply with US law, are unenforceable in practice.
Peter Bradley, deputy director of the anti-bullying charity Kidscape, says: "There's enough evidence from inquests or helplines to show parents aren't scaremongering. With devices getting smaller, it's harder to see warning signs."
Many schools fail to monitor pupils' use of technology, hesays. "It's the biggest issue we have, schools not taking parents' concerns seriously."
But Clarke cautions against alarmism. "I think there is a lot more fear among parents than there need be. Actually, children are quite supportive of each other most of the time. It's the lonely, isolated child we need to worry about. Of course there are issues with bullying - there always have been and there always will be. Technology makes it much more immediate and personal."
- OBSERVER