Author Kathryn Erskine wrote this book in response to the shootings on the Virginia Tech campus, in an effort to explore how the world might be different if people understood each other better. This story about empathy is told from Caitlin's point of view, and will hopefully be a mind-opening read for kids who may know of a child with Asperger's Syndrome. Caitlin functions well academically, but because she cannot interpret emotions in other people, has trouble making friends or interacting socially. She sets her sights on achieving closure after the death of her brother, even though she doesn't have a good sense of what it means. In her simple understanding, she interprets it as seeing her dad smile again. The school shooting is the most upsetting aspect of this book, though it occurred before the story begins. It is referred to several times, but not described. There are many references to the classic book To Kill a Mockingbird, which readers will likely be curious about after reading Mockingbird. This book is best for the more emotionally mature readers in the publisher's recommended range of ten and up.