This unit of the Flexible Learning System (FLS), the third of a 3-volume series on children's thinking focuses on the development of quantitative relations in children between 3 and 8 years of age. The series is based on the application of Jean Piaget's work to early childhood education. Quantitative relations concerns all notions of units and number and their application in such areas as measurement and arithmetic. The development of quantitative relations is examined with the use of conservation tasks which reveal children's gradual understanding that the arrangement of objects does not affect their amounts. The unit is designed for use with a group of adults to help them understand quantitative relations and their organization in preconceptual, intuitive and concrete-operational stages of development. Practice in exploring children's thinking is provided. Activities include thought problems, child interviews, discussions, reading, and viewing a color videotape on conservation from a series entitled The Growing Mind: A Piagetian View of Young Children. Rip-out guided interview forms are provided for all interviews. Also included are an introduction to Piaget and his general theory, educational implications of the theory, transcripts of the videotape, and an annotated bibliography. Related FLS units: "Exploring Children's Thinking: Classification"; "Exploring Children's Thinking: Seriation"; "Working with Children's Concepts"; "Using Toys and Games with Children"; "Developing Children's Sense Perception." (Author/SB)