A new trend of violent assaults, in which teenagers attack unsuspecting bystanders and capture it on mobile phones, has spread to Kent.
The "happy slapping" attack in Ramsgate is the latest in the craze
"Happy slapping" first began as a craze in south London, but has now become a nationwide phenomenon, according to police and anti-bullying organisations.
Footage passed to the BBC showed an assault at a Ramsgate skateboard park.
A school in Tonbridge has also warned that a boy's hearing has been damaged.
Parents with children at The Judd School have been urged to monitor the situation and were told the trend was "most unpleasant and hurtful".
Assaults are videoed on mobile phones and texted to other people
Videos of the slaps are sent to other mobile phones and posted on the internet.
Nicola Kerr, who works for the children's charity Kidscape, said the trend was difficult to control in schools because pupils were not leaving their video phones at home.
"Some schools have tried getting the children to hand their phones into their form teachers at the beginning of each day," she said.
Police in Kent say they have not received any complaints about "happy slapping" so far, but an incident at a Leatherhead school in Surrey last month prompted police to make an arrest and issue a warning.
In London, British Transport Police have investigated 200 incidents in the past six months.
Reported incidents have included a youth approaching a woman at a bus stop and punching her in the face.
A conviction for assault could lead to up to five years in jail.