Real-world High Schools have Dress Codes — no short skirts, no cleavage, no profane slogans — that their students must follow. Even the most liberal public schools have some kind of limits on student attire (even if it is simply "no shoes, no shirt, no service").
Not so in fiction. If a fictional school doesn't have uniforms, there will be no rules guiding clothing at all. Female characters are the most likely to break with reality, sporting cleavage-heavy tops, short skirts and even bared midriffs. In reality, these students wouldn't make it to their first class without being sent home to change their clothes along with being given detention.
Characters who show too much off are Always Female - the guy equivalents are exposed underwear, which has been out of fashion (at least in some areas of the country) since the late '00s and has never been considered effective Fanservice; and T-shirts with "controversial" slogans, which are reserved in fiction for An Aesop about free speech. On the other hand, since baseball caps make lighting someone's face difficult in live-action and are difficult to render through 360 degrees in animation, sometimes a "no hats in school" policy is mentioned to justify their near-total absence.
Subtrope of Dress Code. Can be a result of Hollywood Dress Code, which dictates certain female types must dress in a manner inappropriate to a school setting because of her character type (such as the slutty cheerleader must be dressed skanky or we won't know who she is). Akin to Dawson Casting, as both tropes give the impression that teenagers are much more adult than in reality. Schools like this are likely to have a Sudden School Uniform episode that snaps back to no rules afterward.
- In one issue of Archie Comics' Sonic the Hedgehog that forced the heroes into going into school, Bunnie shows up in an outfit that looks like she raided Daisy's wardrobe!
- In the Robin Series Gotham Heights High School has no discernible dress code with students wearing short dresses, crop tops, spaghetti straps, halter tops, hats, shirts with slogans, excessively baggy pants and all manner of piercings and hair styles without reprimand.
- All the girls who attend Midtown High in Ultimate Spider-Man seem to follow this trope, even Mary Jane, who is supposed to be less popular and even slightly geeky compared to her 616 version.
- In Scary Movie this is lampshaded for laughs. Buffy arrives at school dressed modestly in a cardigan. Once her father is gone, she changes into a Stripperific outfit and attends school that way.
- In Mean Girls the plastics get away with performing in a school pageant wearing sexy Santa outfits that are closer to lingerie than costumes. Also applies when Regina accidentally starts the trend of wearing shirts with holes cut over the breasts. Given that the principal himself raises his hand when asked "How many of you have ever felt personally victimized by Regina George?", this may be an example of how just strong Regina's influence could be.
- In Easy A, Olive is suddenly wearing stuff bordering on bondage gear to school, and for the most part gets away with it. Lampshaded when she asks if she's in trouble since she's never worn skirts that are too short... while the camera is focused on her lacy, spaghetti strapped bustier.
- Most of the girl's outfits in Bring It On, which seem to consist of cropped tops and Painted-On Pants. Even the cheerleading outfits would most likely have gotten them banned from competing.
- Modern-day B-movie American High School is a parody of the modern teen movie, and as such has literally all of its female characters (teachers included) coming to school dressed as if they were headed to a rave (or even an orgy). Even the guys get in on this; most male students at the school are topless 80% of the time.
- Parodied in Not Another Teen Movie with Areola, who is the sexy foreign exchange student. She walks around school completely naked.
- Buffy the Vampire Slayer had a lot of this during the high school years. The skirts were way too short and the tops didn't cover enough. Oddly enough, this mostly applied to Buffy. Even Cordelia was typically more covered up than she was, and even Harmony dressed more moderate than the Slayer herself. Of the main cast, Willow, Tara and Dawn seemed nearly prudish (especially by comparison) and only Anya (a thousand-year-old demon who only looked like a high-school aged girl) even approached Buffy's normal mode of dress. She even wore those sorts of outfits while patrolling, despite them being incredibly impractical.
- Degrassi is/was like this for most of the school and franchise's existencenote and at least three girls over the years have been shown changing from parent-approved clothes into something skimpier in the girls' bathroom before class, beginning with Stephanie Kaye in the Degrassi Junior High days.
- Bianca in Come As You Are pt.1 gets special mention for removing her school polo shirt to reveal a lingerie-like pink tank top mere moments after the principal announces the end of the uniform policy. In Toronto. In January. Talk about putting the "fridge" in Fridge Logic...
- Season 3 of Degrassi Junior High actually had this as a minor plot point and Running Gag. Kathleen wanting to introduce a school dress code is a sign of what a stuck-up prude she is.
- Averted in season 3, episode 3 of Degrassi: The Next Generation, "U Got the Look". When Manny starts dressing provocatively at school to change her image, she gets in trouble for breaking the school dress code. This is basically forgotten about in all subsequent episodes though.
- Teen Wolf's Erica shows up in nearly every scene in clothes that consist of shirts barely covering lacy bras, shirts barely covering lacy corsets, and generally anything that shows off her main assets. For a show that generally eschews traditional high school cliches, none of the teachers have yet to call her out on the stripper wardrobe.
- Saved by the Bell was mostly G-rated, but all three of the primary female characters on the show routinely wore crop-tops, mini's and stripperiffic pants to school (also the odd strapless top, which is never allowed at any school in America, or see-through tops with little more than bras worn underneath).
- Most of Dan Schneider's series include this, be it All That, Zoey 101, iCarly or Victorious. Zoey 101 is probably the worst offender, given that the characters are all under 18 and all of the central female characters seem to be competing to see who can expose the most skin, whether in class or not.
- Parodied in the hit CollegeHumor sketch series, "The Problem with Jeggings."
- The Most Popular Girls in School has one male and one female example; most of the cast who don't wear their high school cheerleading or football team uniform at all times dress fairly conservatively, but Than wear an open jacket with no shirt under it, and Saison wears a backless, midriff-baring shirt so brief that her nip slips come from below.
- In Clone High Cleopatra wears a shirt with deep cleavage and a micromini. Also, Joan of Arc has a belly revealing shirt on.
- Sam of Danny Phantom wears the same midriff-exposing tanktop every day. Paulina and several other girls wear navel exposing outfits as well.
- Kim Possible. Not just the title character herself but her Alpha Bitch rival Bonnie and the rest of the cheerleading squad wear navel baring uniforms that are more appropriate for college and professional sports teams than high school. Even out of their uniforms, Kim and Bonnie wore midriff revealing clothes in early seasons.
- Outfits that Bare Your Midriff are so common among the main characters of Winx Club and the other students at Alfea that you might think that is the dress code. It may help that Alfea is an all-girls school, though at least one teacher took issue with it in a throw-away line. That's not even counting their fairy forms, most of which seem to have a mandated Dangerously Short Skirt.
- Totally Spies! the title characters and many female background characters wore outfits that are more appropriate in night clubs. But for some odd reason, belly buttons weren't visible until later seasons.
- Robotboy had a midriff baring PE teacher in school
- Truth in Television in most German schools. It's practically unheard of for someone to be sent home for their choice of dress.