JenJen:) It all kind of depends. Maybe 10-11 to start with (?). However, there is language (like the n-word, sh*t, etc.) and be prepared to see some racist moments.
Anna The other two people were pretty right about the age group but...I read it when I was ten and I understood everything in it.
Alissa I would definitely say that this book is meant for high schoolers mainly because of the segregation parts and the way the book is written
Melissa I would say fourteen and over. If you are mature, 13. However, I believe that there are a lot of historical events that you should learn first before reading the book, hence the age since I know that the American 50's and 60's are not covered until Junior year of high school (in America).