This volume is the thirteenth in a series of 29 coordinated MINNEMAST units in mathematics and science for kindergarten and the primary grades. Intended for use by first-grade teachers, this unit guide provides a summary and overview of the unit, a list of materials needed, and descriptions of six groups of lessons. The purposes and procedures for each activity are discussed. Examples of questions and discussion topics are given, and in several cases ditto masters, stories for reading aloud, and other instructional materials are included in the book. This volume begins with a review of addition by joining sets and then introduces addition and subtraction on the number line. The use of the addition slide rule is introduced and problems for practice in addition and subtraction are provided. Properties of addition and subtraction are explored, and place value notation is introduced. (SD)