Teen films tend to lean heavily on stereotypes, in fact many teen films build their themes and plots around these stereotypes. The Breakfast Club is a prime example of this, it is a film that exists to examine and undermine stereotypes, however it is far from the only example. Often, teen films will have their entire plot built around characters who want to either become part of, or distance themselves from, a stereotype.
Emo: The Musical follows a character who wants to become part of the emo clique at his new school, and to do so creates an artificial persona for himself which adheres to the emo stereotype. The Duff is a film built upon categorisation of individuals, the main character believes that times have changed in the thirty years since the release of The Breakfast Club, however the inciting incident for this film is her discovery that she is a duff. This discovery leads her to do everything within her power to distance herself from that stereotype. Grease is a film about two individuals from vastly different cliques falling in love, and as a result it relies heavily on stereotypes to create the contrast between the leads. Clueless is a film which defines itself by creating characters which follow established teen stereotypes to drastically exaggerated degrees.
Entire sub-genres of the teen film are built around stereotypes. Nerd films such as Superbad or Attack of the Nerds exist purely to delve into the archetype of the nerd, and their plots often follow a group of nerds trying to escape this stereotype. Teen horror also relies heavily on stereotypes, as can be demonstrated by Cabin in the Woods, a meta-horror in which the victims are specifically selected for their adherence to teen stereotypes.
So what creates this reliance on stereotyping within the teen film?
A central, and often repeated, theme to the teen genre is coming of age and self discovery. Countless stories have been told about the teen who discovers their individuality and becomes a unique person. In order to be able to properly tell this type of story, the characters must have a starting point. More importantly, in order to create the contrast between who the characters begin as and who they become, they must start without the individuality which they develop throughout the film. Telling a story of self-discovery, a central theme in the teen genre, require that there be something beneath the surface of the character to be discovered. For this reason teen films will often establish their characters as conforming to established stereotypes before showing how these stereotypes are constructed, that they aren’t representative of who the character really is.