Flat Stanley by Jeff Brown
Flat Stanley is a creative story of a boy who suddenly is flattened when a book shelf falls on him. In the book, Stanley showcases all of the advantages of being flat. He can tour the world in an envelope via the pen pal system. This book has been a classic for many years. I remember my sons both studying the United States Postal System while reading Flat Stanley and learning to write a letter that would be mailed in the USPS.