This book is one of a series of children's biographies about famous Americans. One of the best things about their subjects is that these are Americans that haven't already had myriads of books written about them. George Washington and Abraham Lincoln are not in the bunch. This particular book, John Hancock, is just one such example.
John Hancock grew up rubbing elbows with Paul Revere and Sam Adams in Boston, the hotbed of patriots prior to the Revolutionary War. It gives good general overview about life in those days. For instance, boys wore the same gowns as girls until the boy would go to school, around the age of 6. It has lots of such little details about life in those days for a boy growing up.
The writing style and content is perfect, I would say, for mid-elementary age students, although I did not find an age range specified on the website. Along with the book, the website has links to online resources for more information on John Hancock and has a downloadable and printable Teacher's Guide and Webquest with extra activities to go along with the book. This will help the interest in the book. My 5th grade son did not find the book particularly interesting, although he did read the book in its entirety.
I would recommend it as a resource for early American History for finding out more about the man who originated the expression about, "your John Hancock" in reference to signing one's signature.