A tablet might also be called a book, but it is only one or two pages. And since tablets are usually made of clay or stone, they would be pretty heavy in your bookbag.
This is a tablet from Sumer, the country known as Iraq today. The writing on it is called cuneiform. This tablet was made in 2001 B.C., more than 4,000 years ago.
Photo courtesy of The Melbert R. Cary, Jr. Graphic Arts Collection