For me it was Gerald’s Game by Stephen King. I think it’s a fantastic novel with amazing character development. The main character is extremely realistic and well written. Despite the seemingly silly premise, I was invested throughout the entire thing. The main character’s development is really what sells it for me.
That being said, I am absolutely not reading it again anytime soon. There are two scenes in particular(if you’ve the book I’m sure you know) that managed to make extremely uncomfortable, mortified, and disgusted. My biggest fear is being trapped and helpless, so this book really got to me. Fantastic book, I’m never picking it up again.
Either that or Lord of the Flies… Dear God.
I loved having good teachers giving us good books to read. I remember being one of the few in class that actually read the books, while the others mainly looked up summaries on internet. That one teacher that gave us Lord of the flies wasn’t very good, but I’ve had some that were like you describe. The best book I had to read for class was probably The Stranger by Albert Camus, when I was 15 to 16