This book is an extension of the 1966 film/text series (ED 018 276) from the National Council of Teachers of Mathematics and was written to accompany 12 new teacher-education films. It is strong enough, however, to also serve alone as a text for elementary school teachers for the study of rational numbers. The 12 chapters corresponsing to the films were written separately by committee members with various methods of presentation. Aspects of rational numbers covered include a rationale for their introduction; the four operations with positive, decimal, and negative rational numbers; measurement; and graphing. (JM)