This book is a collection of papers presented at the symposium, "Conference on Ordinal Scales of Cognitive Development, sponsored by the California Test Bureau. Papers include: "The Theory of Stages in Cognitive Development" (J. Piaget); "Two Approaches to Intelligence: Piagetian and Psychometric" (D. Elkind); "An Implicit Metric for Ordinal Scales: Implications for Assessment of Cognitive Growth" (P. M. Bentler); "Theoretical Regularities and Individual Idiosyncrasies" (R. D. Tuddenham); "Some Problems Associated with Formal Thought and Its Assessment" (K. Lovell); "The Role of Experience in the Rate and Sequence of Cognitive Development" (M. L. Goldschmid); "Does the Piagetian Approach Imply Instruction?" (S. E. Englemann); "Developmental Theory and Diagnostic Procedures" (B. Inhelder); "Developmental Stages and Developmental Processes" (H. Beilin); "The Uses of Verbal Behavior in Assessing Children's Cognitive Abilities" (J. H. Flavell); "Closing Remarks" (B. Inhelder and J. Piaget). The following papers were not read at the conference, but were presented in written and outline form respectively: "Montonicity Analysis: An Alternative to Linear Factor and Test Analysis" (P. M. Bentler); "Assessing Cognitive Development via Measures of Optimal Performance" (J. D. Ayers). Comments and open floor discussions on each paper are included. (MS)