This one shocked me. Romeo & Juliet can certainly be read & understood by an advanced 8-10yo reader but is absolutely thematically inappropriate.
The most "questionable" reading assignment for us was Stephen King's IT (7th grade). I had already read it (IT?) on my own so I was thankful that I could just skip over the parts I did not like, all of which I remember vividly to this day despite only reading them once

I think there were some complaints but the book is still in the curriculum.
But, the one I had the worst time with was The Grapes of Wrath. I ended up sobbing in the counselor's office after class because I wanted to hug my grandma, and I was 15 years old. You never know what's going to get to you, at any age.