This is part one of a two-part SMSG mathematics text for elementary school students. One of the goals of the text is the development of mathematical ideas via appropriate experiences with things from the physical world and the immediate environment. The text materials provide an introduction to the study of mathematics in which growth is from the concrete to the abstract, from the specific to the general. The authors emphasize exploration and progressive refinement of ideas associated with both number and space. Chapter topics include: (1) sets of points; (2) addition and subtraction - review and extension; (3) describing points as numbers; and (4) arrays and multiplication. (MP)