naked school attendance
A subset of the zenra fetish involving students who are either not wearing certain clothing items (being topless, bottomless, etc.), wearing a revealing school uniform, or simply being nude, with the students being oblivious to their state of undress or treat it as a normal activity.
Typically, the setting treats these impractical "uniforms" or nudity as their "school uniforms". Other settings might instead have a "nudity day", a special school day where all students and teachers must attend the school naked.
This is not limited to classrooms, as it also covers the commute to school these naked students take, often within the presence of other people who are otherwise wearing normal clothes. If it is the latter case, then the tag nudist and/or exhibitionism is applicable depending on the context.