Sheila and the Magnificent Tail
I'm going to suggest that this book is best suited for the 4 to 8-year-old age group. (Full Disclosure: My 6-year-old son tracked well with it, but my 4-year-old daughter got fidgety by the halfway point and seemed to miss the moral of the story.) The book is fairly long, and the word count more dense than I would have expected. The author doesn't skirt big words, but doesn't abuse them, either.
The illustrations were bright and captivating, without distracting from the emotional focal point. And it's ultimately the emotional journey and character growth that make this such a potentially poignant story. It's a beautiful allegory for the age-old principle: "It's what's inside that counts."
I could see this book being a potent tool for building both coping skills and empathy in children of this developmental range.