Simon is having a bad day because his sister gives him a strange hair cut and his friends tease him, but he runs into Grandma Rose who teaches him how to handle teases and put-downs.
This book is essentially standing in to do what most parents don't do: teach kids how to stand up for themselves/others.
If I had this when I was a little kid, I probably would have better stood up for myself using these tips.
But what would have really helped me to stand up for myself, would have been to go through those types of situations (harsh, I know) and then read this book, to better solidify my arguments/defenses, given my experience & knowledge (and technically PREP).