Mark Spess' book about clay animation. It goes into great detail about every aspect of animation. It is aimed at the professional and tends to be over the heads of beginners. It is a wonderful resource, though.

http://www.animateclay.com/howtobook.htm

Creating 3-D Animation is an outstanding book. It covers everything from the history of animation to the process in professional studios. Stop animation movement is comprehensively covered and is easily adapted to classroom instruction. This is written by the same artists that created Morph, Wallace and Gromit, the Dancing Raisins and Chevron commercials!

Clay Sculpting for Digital Media by Stephanie Reese (Paperback)
www.amazon.com

The Clay Animation Kit from www.tech4learning.com is an excellent place to start. It has a small steo-by-step book for using their software (Imageblender) for the animation process. It even comes with a small sample of clay, wire, and tools. For a teacher starting with clay animation, this is a safe starting place!

Clay Kit at Tech4Learning

Clay Animation; American Highlights 1908 to the Present by Mic Frierson, Michael Frierson www.amazon.com 

Polymer Clay: Exploring New Techniques and New Materials by Livia McRee, Celie Fago, Georgia Sargeant www.amazon.com