In the winter of 1965, an experimental course in Elementary Number Theory was presented to a 6th grade class in the Hosmer School, Watertown, Massachusetts. Prior to the introduction of the present material, students had been exposed in class to such topics from the University of Illinois Arithmetic Project as lattices, number lines, frame equations, and linear affine transformations. The present materials are concerned with such mathematical concepts as (1) fundamental operations involving integers, (2) division of integers which included remainders, factorization, and the Sieve of Eratosthenes, and (3) number systems in bases 2, 7, 10, and 12. Teacher and student materials that were used for a period of 14 weeks are included. [Not available in hardcopy due to marginal legibility of original document.] (RP)