Theoretical and empirical research derived from Piagetian theory is collected on the intellectual development of the elementary school child and his acquisition and utilization of conservation concepts. The articles present diversity of method and motive in the results of replication (validation studies of the description of cognitive growth) and efforts at modifying the course of growth as charted by Piaget. Research is included on quantity conservation concepts at different ages and with situational generality, the development of number concepts (including a scalogram analysis and a comparison of the logic of classes and cardinal numbers), the development of spatial and geometric concepts (also examined by nonverbal methods), and the growth of logical operations (including a scalogram study). Additional areas treated are the acquisition of conservation of substance and weight, quantity, number, learning and operational convergence in logical thought development, effects of verbal and perceptual training on water level representation, and Piagetian research and education. Conservation is discussed theoretically as a source of empirical research, by a stimulus-response analysis, by problems from perception to inference, and on methodological and definitional considerations. (SN)