I'm confused as to what you are implying Trekkie, I don't see school girls as sexy. I do think they occasionally through peer pressure, or more likely media pressure attempt to appear "sexy" with their clothes over use of make up etc. If this isn't the case then there is really no reason for us to argue the let girls be girls campaign. Let them all walk about in padded bras, thongs, I remember a children's store selling crotchless knickers in Colorado last year....
The fact is, little girls may feel a pressure to dress a certain way, or maybe they want to dress a certain way... in whatever the case it is up to adults to say this isn't necessary. You are in school to learn, to be comfortable and to wear comfortable appropriate clothing. I can't go to work in a mini skirt it because it isn't appropriate.
There should be no gender bias in school clothing and they should wear what make sense. Loose trousers make sense, you can run, jump, trip over etc. they were designed for movement. Dresses restrict girls and women we may choose to wear them but they awfully impractical items of clothing. They were designed to be looked at not to do. Tight trousers are again impractical and can cause thrush. I really can't see any reason for adults to encourage this.
In fact I really would like for us to look at clothes in general, and why men still start the day tying a noose around their neck, and why children in schools should have to. Again it isn't practical clothing.
My children go to a no uniform school, and mostly what all the children wear is jeans and a t-shirt/hoody or similar variations. In the summer they wear shorts. Some of the girls wear very short shorts. It doesn't seem to be considered a big deal (school dress code is no spaghetti straps, no swear words or gang colours and that's about it). We've not come across much clothes related bullying as of yet and it's nice for the children to wear clothes they like and are comfortable in.
I remember my school uniform being uncomfortable as if fitted very badly, and being ugly as it was made out of nasty material. Smart it was not!