The paper presents reasons for teaching topics from number theory to elementary school students: (1) it can help reveal why numbers "act" in a certain way when added, multiplied, etc., (2) it offers drill material in new areas of mathematics, (3) it can develop interest - as mathematical enrichment, (4) it offers opportunities for students to develop ideas of inductive and deductive reasoning, (5) it offers patterns which can be discovered, (6) it offers unsolved problems of mathematics, and (7) it lays a foundation for future work in algebra. Examples from number theory discussed include history, number patterns, prime numbers, unsolved problems, and divisibility rules. (JC)