This volume is the third in a series of 29 coordinated MINNEMAST units in mathematics and science for kindergarten and the primary grades. Intended for use by kindergarten teachers, this unit guide provides a summary and overview of the unit, a list of materials needed, and descriptions of four groups of activities. 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 unit deals with sets of objects, with problems of classification and description of objects, and with comparisons of sets. Activities described use property blocks and other objects in game, puzzle and story situations to develop conservation, and the basic notions of set theory. (SD)