Her family is very positive about her wants, and they cater to her wishes without making a fuss or being critical or hurtful. They just want her to be happy with who and how she is. As she grows older and interacts with friends in school though, things get tense. The young children and adolescents she encounters in all her schools (elementary, middle, and high) and in her neighborhood are not always the most accepting of her toy, wardrobe, playtime, or pastime choices. And from these points of conflict come a discussion about what's right, who gets to decide what is right, and how people judge one another based on preconceived gender roles.
All of the reviews I have read about this book have been full of praise. The notoriously tough Kirkus Reviews gave it a starred review and called it "Spectacular; a book to make anyone think seriously about society’s preordained gender role." The School Library Journal's Amanda MacGregor called it "utterly fantastic." For those interested in learning more what's behind this book, Prince talks about her work on Tomboy in this interview with Comic Book Resources.
Going by the tried and true Joe Bob Briggs 3 B's scale, this book has 7 beasts (three bullies, three mean girls, and one crazy "friend"), a few mentions of blood (menstrual), and 3 boobs (in an educational film the girls have to watch in school). It also features some profanity, harsh taunting, and more than a few romantic or sort of sexual situations, so I recommend it for readers mature enough to handle those things.
Tomboy was published by Zest Books, and they offer a preview, reviews, and more here.