The annual conference of the Girls' Schools Association has heard that technology and peer pressure put young girls at risk of being subjected to cruel comments "24 hours a day".
Jean Gross - the UK's "Communication's Champion" for young people - says social media and texting have given girls more ways of excluding each other.
"Anybody who's been a girl knows that girls can often make each other's lives a misery in school through communication, through this business of forming of cliques and of being one minute 'you're my best friend' and the next day, suddenly, 'you're not my best friend, I've got another best friend'.
"Now girls have got even more ways of excluding each other through communication, so they used to do it just through verbal language, now they can do it through texting and de-friending and all of those things."
Mrs Gross said that technology allowed girls to keep up this behaviour "24-seven":
"Some of my friends who have got girls inside school now say that you can't get away from it, you go home and it's there."
Mrs. Gross says she believes girls don't "know quite how much it hurts, because the people who may be doing it, it may not happen to them, they're protected..."
She said teachers can play their part in teaching girls about this kind of bullying: "Teachers can teach some of the skills of say, not following blindly, you can teach assertiveness, you can teach girls about this kind of bullying, teach them to understand it."
Mrs Gross also suggested female students read and discuss the Margaret Atwood book, Cat's Eye, or the film Mean Girls, both of which are about girls excluding each other.
"I would advocate that you actually spend time exploring some of these issues with girls rather than just say 'girls will be girls' and it's always going to be like that," she said.
What do you think?
Has technology made girls' bitchy behaviour worse?