Yeah, it depends on the situation and the people.
Sometimes other approaches work best, like ignoring... Even then, it's good to ignore with an assertive posture and sort of like you have a purpose to go somewhere and just don't want to be bothered. Sometimes it helps to look grim or annoyed... (Maybe people won't dare to mess with you then..) and busy, like you're rushing to a meeting or have a clearly defined purpose..
It can also help to find allies... Do you have any other people who could just by their presence stop any untoward behavior?
Like if it's two or three of you together, or more, some people won't dare do anything... Some are really cowards and only 'attack' when a person is alone.. like dogs... some bark at one person, but shut up if it's three people together.. Can you connect with other people? Maybe other loners or other friendly and nice people? Maybe even the librarian or the cooks or the janitor man (if those are sort of recpected/feared a bit by the bully girls...?) or any teachers that don't have problems with them...
Sometimes joking can help, humor can disperse situation.. It depends what happens and how.. And how you go about it.. I was never harassed by girls, so don't have any good answers.. I might tell'em, 'You got a crush on me or something?' (When we were little, sometimes little boys teased the girls they liked, or such..) Though not sure if this wouldn't provoke them more, lol.. I'd probably just laugh it off.. if possible..
When does this happen? In what kind of situation? What happens exactly? Who are these girls - 'the elite' or 'bitchy punk/rockstars' or...?? Do they ever get into physical fights or just talk? All things to consider..
Do you have a school counsellor or trusted teacher that could help? (Or parent/sibling that could yell at them and tell'em off?) Is there an anti-bullying program at the school? Also, how old are you, girl or boy, and what kind of school is it? Might help to give you any more answers/ideas...