I saw the movie, then went out and bought the book. I sat down and read the book cover to cover in one sitting; I couldn't put it down. It's true that this book has not been prettied up. There is harsh language, there is sex, and there is drugs. But the writers don't glorify sex or drugs. They speak honestly about their lives, including their struggles with addictions, abuse, pregnancy, and above all, violence.
The book works because it is real. Erin Gruell's teaching worked because she allowed the students to be real, to be honest, and to be themselves. If anything, the movie downplayed Erin Gruell's accomplishments. From the book, one learns that she started her efforts to reach out to the students, including working a second job, when she was still a student teacher, a time during which most teachers, even in "safe" suburban schools, are just trying to survive day to day. The book also points out that there were 150 "freedom writers" in five classes, not the one small class shown in the movie.
I have been teaching at the high school and college level for ten years. I highly recommend this book to anyone who is honestly interested in making education a more meaningful experience for the students. It's true that parts of the students' lives are not pretty. But that is exactly the point.