I'll bet that it isn't any more.
“Ivan Denisovich”
While not required reading, I read it on my own while other boys were reading about teens and hot rods.
I don’t understand it but in my teen years (1959-1966) I preferred more adult oriented books than teen novels. I even managed to get the librarian at the Carlsbad NM schools to issue me an adult card. I was 14 at the time.
In those years, reading was the only thing that kept me sane.