Gotham High (lost production material of cancelled Batman animated TV series; 2009)
Gotham High was the concept behind an animated TV show about a teenage Bruce Wayne attending high school with his future enemies and allies.
When creator Jeffrey Thomas drew a picture of a young Joker and Harley, DC liked it enough to order an entire series based on the concept.
The plot would have Bruce Wayne attend High School with Barbara Gordon and his entire Rogues Gallery. Each character would have represented a social clique (The Riddler was a nerd, Killer Croc was a bully, Mr. Freeze was the "cool" kid, etc.).
The series was cancelled for reasons unknown.
It is possible that elements of the show were reworked into the web series DC Superhero Girls which also involved teenage versions of DC characters attending high school. This show also featured characters from the Batman franchise.
Gotham High (graphic novel)
It is also possible that elements of the show were reworked into a graphic novel of the same name written by Melissa de la Cruz and illustrated by Thomas Pitilli released by DC Comics in 2020, which was about the relationships between Catwoman, Batman and Joker as high school teenagers in a love triangle.
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