What one book do you believe NEEDS to be taught in school?

This post is part of the GRAB(ook) Club, an online book club open to anyone where you can drop in and out as you wish.  However, you do not need to be part of the book club to comment; I'm curious about everyone's opinions.

This month's selection was To Kill A Mockingbird, by Harper Lee.  I'm guessing that for most people this was a reread, but for me it actually wasn't.  I never had to read it in school and never ended up picking it up after that.  There's a lot of books like that for me.  I've never read anything by J.D. Salinger, William Faulkner, F. Scott Fitzgerald, Alice Walker, or any number of other classic authors.  Some, like Ray Bradbury and Kurt Vonnegut, I've picked up on my own, but plenty of others I haven't so far.

I'm not sure why To Kill A Mockingbird wasn't part of the curriculum for me.  I don't know if it was because of the use of the n-word throughout, or if they thought it wasn't necessary because we covered other female authors and people writing about race relations or what.  I will say that I would have gladly traded this for Invisible Man with regards to books discussing racism.

I liked the character development and descriptions a lot more in To Kill A Mockingbird, as well as the way that Lee handled people understanding or not understanding Scout.  But also, I find To Kill A Mockingbird much more appropriate for the high school age group with how it handles sexual content.  I suppose at least part of that comes from it being written from the point of view of Scout, with an eight-year-old's understanding of sexual matters.  No matter how or why it was done this way, though, the question of and description of rape was managed delicately enough that I could have handled it in high school and had read worse on my own.  Invisible Man, on the other hand, skeeved me out in high school with the graphic descriptions of the naked women in the Battle Royale scene.  I wasn't ready for it, and I was disturbed by it.  The rest of the book I was just bored by, but I squirmed both mentally and physically when I read that part.  Yes, I believe that assigned reading should broaden our horizons and make us think about things we might not have otherwise.  But I also believe, now that I've read it, that To Kill A Mockingbird would have been a better choice for making students think about the past and what is still here in the present in a new way.

So what do you think is just that important in classic literature that it NEEDS to be taught to students?  And what about that book/play/poem/etc. makes it that important?

After you answer my question, please click over to read the rest of the book club questions for To Kill A Mockingbird. You can get your own copy of To Kill A Mockingbird by Harper Lee at bookstores including Amazon.