By Katherine Sellgren
BBC News education reporter
Girls are becoming increasingly violent when they bully other children, a university study suggests.
Girls are said to be becoming more physically aggressive
Researchers from Brunel University highlight the growing phenomenon of the "girl gang" and warn this is leading to more aggressive behaviour among girls.
The study also indicates that bullies are becoming more sophisticated in terms of using phones and internet.
The research findings follow two separate violent attacks on girls in secondary schools.
Earlier this month, Natashia Jackman, 15, was attacked with a pair of scissors at her school in Surrey and, in October, Shanni Naylor needed 30 stitches in her face after an assault at her school in Sheffield.
Dr Sally Henry said the differences between girls' and boys' bullying style were now becoming blurred.
"Whilst girl bullies have traditionally focused on the psychological side, with boys tending towards the physical, gender roles have now become blurred," said Dr Henry.
"Girls are increasingly violent - and boys use both forms of intimidation. This means schools have an increasingly tough job to detect bullying and deal with it."
She said the aggressive stance adopted by women in many music videos promoted "acting tough".
Dr Henry also raised concerns about the influence of soap operas on young people.
She said characters such as the Mitchell brothers in East Enders could encourage intimidating behaviour.
"My research shows that it's pretty much a case of 'like father, like son' - kids learn how to deal with difficult situations from adult role models like their parents.
"But, in the absence of parental guidance, kids will look to other role models - for example, male characters in soap operas.
"With around 35 million people a week viewing soap operas like EastEnders, Emmerdale, Coronation Street and Hollyoaks, this is a real problem."
Dr Henry suggests bullies should be sent on anger-management camps.
"There should be no stigma attached to these camps - they would simply be an opportunity for children to learn how to deal with their emotions effectively, rather than take them out on others."