I want to thank the many educators and authors who shared their expertise to make this book possible. Their books and articles are listed in the Bibliography. My husband, Sam Zaslavsky, took all the photographs and helped in many other ways. Thanks to J. Weston Walch, Princeton U. P., and Marcia Ascher for permission to publish. Also thanks to Mr. and Ms. Abelson, Ms. Schnipper, and Mr. Smith for use of their photographs, and Dr. Crowe and Dr. Gerdes for use of their drawings. I take full responsibility for any errors or lack of clarity.