This unit of the Flexible Learning System (FLS), the second of a 3-volume series on children's thinking, focuses on the development of order relations (seriation) 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. Seriation concerns the way children reason about relationships between elements of a series or sequence. The unit is designed for use with a group of adults to help them understand order and its organization in the preconceptual, intuitive and concrete-operational stages of development. Practice in exploring children's thinking is provided. Activities include thought problems, role playing, child interviews, discussions, reading and viewing a color videotape on seriation 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, seriation materials, a transcript of the videotapes, and an annotated bibliography. Related FLS units: "Exploring Children's Thinking: Classification"; "Exploring Children's Thinking: Conservation"; "Working with Children's Concepts"; "Using Toys and Games with Children"; "Developing Children's Sense Perception." (Author/SB)