Why do we still try to control how teenage girls dress?

Last month on Instagram, Kim Kardashian West posted a year-old picture of herself standing naked in her marble bathroom, with the caption: "When you're like I have nothing to wear LOL". The post received more than 250,000 likes and 130,000 retweets.

Then Rowan Blanchard, star of Disney's Girl Meets World, weighed in. "I think that is an awesome thing 2 teach girls," she tweeted. "To be accepting of yourself and use the selfie to choose how you want to be viewed & to try to gain control of your own image: something girls have never had (or control in general)".

Rowan Blanchard is 14 years old.

Is sharing a naked picture on the internet "an awesome thing 2 teach girls"? Many people over a certain age would say "hell no", but Blanchard's response is typical of a generation of young girls who - thanks to social media - are well-versed in feminist theory and not particularly interested in your opinions about how they should dress. And nowhere is this truer than at school, one of the major places where this generational schism plays out.

Classrooms have become battlegrounds where dress code wars are fought. Earlier this month, Henderson High called 40 Year 11 students to a meeting where they were told their uniform skirts were deemed too short. The reaction was swift, with teenage girls outraged that they and their knees were being blamed for "distracting" the boys.

Many criticised the school on Facebook. Sample comment: "Oh dear, the old thinking is still out there. Come on people, we need to give our sons and fathers a bit more credit than that."

In America, schools have banned or regulated short shorts, tank tops, miniskirts, leggings, yoga pants, skinny jeans, crop tops and halter tops, removing girls from class, handing out detentions (in one school, these were 90 per cent female) or making students change into a "shame suit" designed to humiliate its wearer.

Again, in most cases, the explanation given is that tight, brief or revealing clothing is "distracting" for male students and teachers. Cue staged walkouts by young female students, "Crop Top Tuesdays" and organised protests under the social media hashtag #iammorethanadistraction.

At Western Springs College, one of the only mufti high schools in Auckland, a Young Feminists group formed after some students felt that a female teacher was enforcing the school's dress code in a way that discriminated against girls with big breasts.

Matilda Boese-Wong (18), who was in the group but has since left school, says being told you're a distraction to boys is unfair. "It's not my fault I'm sexualised to that point. And if it's not fair, you've got to do something about it."

The dress code was revised after negotiation with school management and parents. A couple of months later, when a Year 11 girl was cited for dressing inappropriately, it was amended again.

"She thought it was because she was not wearing a bra," Boese-Wong says, "but it was because she was wearing a T-shirt that was cut low at the sides, so if you were looking from the side, you could pretty much see her boobs. I do think that, for a learning environment, that's probably a little bit much."

Western Springs' dress code now states that clothing should be "appropriate for all school-related occasions", that anything "immodest, ripped or that has offensive messages" is not acceptable, and that figuring out what's appropriate is "part of the education process".

The most controversial item of clothing currently popular with this great country's teens appears to be what Western Springs' associate principal Ivan Davis describes as "really revealing shorts that reveal butt cheeks" or what fashion marketers call "cheeky shorts" that reveal "underbutt". Singer Miley Cyrus and reality television personality Kylie Jenner are fervent fans.

Why do teens wear booty shorts to school? Maybe it's because they want to be sexy. Being physically attractive is a rare source of power for young females. Or maybe they just like the way it looks.

"Sometimes it's just that a trend at the time is this item of clothing that just happens to be quite revealing," says Boese-Wong. "I do get that those trends come from companies who are basically contributing to the sexualisation of young girls, [but] for a lot of teenagers - boys and girls - fashion is a huge way of expressing yourself. Sometimes it's nothing to do with wanting to be sexual. My style is something I care about a lot and I'll wear an outfit that might be revealing, but I'm not wearing it for that reason."

"Normally when they're confronted, they're quite shocked," Davis says. "This is the teenage brain: it just doesn't occur to them."

Beyond the safety of the school grounds, many parents fear that if their teen wears revealing clothing, they'll attract the attention of sexual predators. It's an understandable fear, but not one grounded in the reality of sexual violence in New Zealand, where one in three girls will be sexually assaulted by the age of 16. A young person is far more likely to be assaulted by a trusted adult or relative, or even a classmate - New Zealand research estimates 90 per cent of sexual violence is committed by someone known to the victim. How they're dressed is not a contributing factor.

"The reality is that sexual assault is caused by the attacker's power and control issues, rather than uncontrollable sexual urges due to stimulation because of what the person is wearing," says Debbi Tohill, director of Rape Prevention Education.

Tohill says parents worried about protecting their kids from sexual violence should talk to both sons and daughters about what consent means, and make sure they understand that everyone is responsible for their own sexual responses.

There is one good reason for schools and parents to give careful consideration to what teenage girls wear to school. In the late 1990s, scientists performed an experiment where students were asked to put on a swimsuit, then do a maths test.

The male students said they felt silly, awkward and foolish. Some could be heard laughing from the changing room. Their performances on the maths test were unaffected.

The females reported feeling disgusted, angry and ashamed. Although alone in the changing room, they still somehow felt "on display". Their performances in the test were significantly decreased.

The scientists theorised that women are socialised to objectify their own bodies, and that this "self-objectification" taxes their attention span and mental resources: girls can't concentrate fully if they're worrying about how they look and, in a culture that puts undue emphasis on appearance, worrying about how you look isn't a choice, it's a survival skill.

This is the world we've made for our girls. It could be part of why girls' maths ability appears to decline around puberty. And it's why, perhaps, teenage girls ought to be discouraged from wearing notably body-revealing clothes to school. Not because it's distracting for males, but because it's distracting for themselves.

The American Psychology Association, which researches the sexualisation of young girls, has some supremely practical suggestions for parents worried about their daughter's outfits.

First, if you see youth-focused brands putting undue value on sexiness, call it out. Teach your kids to be enlightened consumers who are mindful of sexualisation.

Second, teach boys "that girls deserve dignity and respect, no matter what they wear", and expect that they can and should control the urge to perve.

And if you want to question what your teenage daughter wears to school, don't focus on what it will do to boys or how she will be perceived by others. Instead, ask her whether her clothes are going to be comfortable enough for everything she wants to do today.

What teenagers and their mothers really think

Nganeko Newman (14), a student at Western Springs College, and mum Royala Newman, a social worker.

NGANEKO:

I wear really basic stuff. I go to Glassons and Cotton On and malls to look for anything comfortable. It's gotta be black or white.

If I wanted to impress someone, I'd probably just wear black skinny jeans or my black jumpsuit that I wore for school prizegiving.

I change my style quite a lot. I wear tight, cropped halter singlets with trackpants or a denim skirt and Converse shoes or some Superstars. I like tight stuff but I make sure it doesn't look too ...

Mum will give her honest opinion and if it doesn't suit, she'll tell me.

She'll say, "You look a bit summery," or "You look like you just rolled out of bed." I kind of understand.

I went to McDonalds and there was a girl and she had shorts [with buttock crease visible], and my friend went up to her and said: "Your shorts." And she went: "Yeah?"

"We can see your bum."

"Yeah?" We just told her 'cause we thought she didn't realise. But she did! She knew! We went: "Do you want people to see it?"

And she went, like, "Yeah!"

This year, a lot of girls are self-conscious about being fat. They'll go swimming, but in a big T-shirt or whatever. We had a class swim and the ones who thought they were quite big sat out and got really upset. I hate it when people feel bad about themselves.

ROYALA: I haven't really been too strict on what [Nganeko] wears, because I already know what clothes she has, anyway.

There were some really short shorts that bothered me. I saw quite a few of those at her school last winter. She's allowed to wear them around home or if she went to her mate's house, but not to school. I guess it's because she's travelling from here to town to Western Springs and there's quite a lot of people in that space, so I wouldn't want anybody checking her out.

It's more a safety thing. I feel insecure for her, and protective.

I try to make her change and I usually go and moan about it with her dad. He usually just says, "I don't know. You're the woman."

Xanthe Brookes (16), a student at Green Bay High School, and mum Jeni Little, a music teacher there.

XANTHE:

We got this letter a while ago about how no one was following the dress code. There were three lines of rules for girls and one line for boys. But all the teachers say different things. Some say it's distracting; some say it's so we

can have a more professional environment.

But people are still just wearing trackpants and exercise clothes, which don't reflect professionalism at all.

I get my sense of style from my mum - she lived in the Cook Islands and wears lots of influences from cultures with non-Western beauty ideals - and from female musicians.

I like watching couture shows. The fashion industry is so interesting. I follow lots of cool designers on Instagram. Having lots of different sources to take influences from means you're not restricted to one standard. If you're exposed to a narrow set of media, you're going to have a warped idea of what's beautiful and what's sexual.

A lot of people see an image they think is sexy so they'll buy all these things to try to fit it, even though it doesn't suit them. It's like when you get a haircut and you take in a picture but obviously they can't make it look exactly like the picture.

You see people change [as they get exposed to more]. In Year 9, they'll come in looking like everyone else, wanting to feel like everyone else, but by Year 11, they'll have listened to different music and stuff and changed their outlook on fashion. Intermediate was where I felt more societal pressures but by high school I felt more in control of my fashion.

I play roller derby, and that helps. It's lots of strong women in training bras, all different weights, and they don't care because their body is doing what they need it to do. It's one of the only things that I've ever found that's made me want to be bigger, to have more muscle. Also, going to gigs and seeing female musicians just being totally okay with sweating.

JENI: Xanthe's generation have fantastic body confidence. They don't spend a lot of time hating parts of themselves. That's quite a joy to see, because it was a lot different when I was a teen.

In Year 9, she probably did her hair every morning with the straighteners. Now, she's happy just to get up and go.