No Dress Code

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 wear uniforms, there are 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 after being given detention.

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.

Film

 * 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.
 * In Easy A, Emma Stone's character is suddenly wearing stuff bordering on bondage gear to school, and for the most part gets away with it.

Live Action TV

 * 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.
 * Degrassi was like this for most of the school and franchise's existence 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.
 * And Degrassi Junior High as well.

Web Comics

 * In Bridges, Alyson shows up for her first day at school in a corset and miniskirt that would be more suitable to a night club.

Western Animation

 * In Clone High Cleopatra wears a shirt with deep cleavage and a micromini. Also, Joan of Arc has a belly revealing shirt on.