Grandfather Tang's Story by Ann Tompert is a wonderful folktale and math book for kids. It is perfect to introduce during a geometry unit when learning about 2-D shapes.
This book highlights a wonderful relationship between a grandfather and his granddaughter.
In the story two fox fairies keep changing their shape. A tangram (an ancient Chinese Puzzle that is a square divided into 7 pieces - each called a tan) is arranged and rearranged to represent the various characters in the book.
This is a great read-aloud book for kids. I would suggest that the first time it is read to kids that it just be enjoyed in its entirety and discussed with the kids.
With subsequent readings, students can follow along with the story and recreate the animal characters with their own set of tangrams. A pattern for the tangrams is included in the back of the book.
Later the book can be placed in a math or reading center for students to use independently or with a partner.