Snitch by Allison van Diepen.
About Snitch: A girl is branded as a snitch at her inner city high school.
van Diepen did an excellent job of showing that the decision to join a gang isn't always easy and that, while gangs are not good, they aren't completely evil either. K & I reviewed this book together. Full review: Snitch by Allison van Diepen
This was for the 2nd Canadian Book Challenge.