Reading Grade Level vs Content

Have you ever a read a book, and after you complete it you think, "That was amazing." That's the way I felt about The Perks of Being a Wallflower by Stephen Chbosky. While reading this book, I wondered what grade level could I use this book in the classroom, then the sexual content increased, and I knew I could never use this book in the classroom. This would cause parental uproar.
Looking at the grade level of this book, I discovered that it is a 6.1 grade level. Sixth grade? It's crazy how books are classified just by the difficulty of the words and sentence structure. This book should never be read by a 6th grader, and I'm not sure I would be comfortable having juniors or seniors reading this.
I chose to read this book to base a diversity project on. I have to create a webquest that will assess student knowledge. Going into this, I am going to base my assessments off the fact that juniors or seniors will be reading this for class.
This book explores so many things that some kids actually experience like rape, molestation, and just finding a friend and fitting in. Reading through this book, I wondered if Charlie has autism or Asperger's because he cannot focus his thought process and he frequently cries when nervous. Later, we find out what happened to Charlie, and possibly his "home life" has something to do with his behavior.
Something I loved about this book, was the music incorporated into so many things. Teenagers usually associate some event in their life with a song, and Charlie's experiences were no different. There are many analysis I could have students do based on the song listed in the book. Also, students could compare the film to the book, which is a standard. I have not seen this movie yet, but I might find certain scenes and have students compare the movie scene to the book and explain how they were different and could be improved upon.
This book was touching and realistic, and it left me wanting more. Who is Charlie writing to? How does Charlie get through high school with his friends gone? Is Charlie ok? I would recommend this book to anyone over the age of 18, but I would never tell a 6th grader that this book was appropriate for him/her to read even though it is considered a 6th grade level.