The Drifting Classroom is a Japanese horror manga series published from 1972 to 1974 that follows a school (and its students) that is mysteriously transported through time to a post-apocalyptic future.
Everyone knows about Junji Ito but not many people know about the work of Kazuo Umezz and that’s a shame.
This manga falls into one of my preferred manga sub-genres “kids suffering greatly and no one knows why” (Bokurano by Mohiro Kitoh is a great one of these). The story takes place in a classroom that’s drifting… If you’re a fan of Junji Ito’s work like Uzumaki then you should check this one out too.