The author attempts to analyze and synthesize the literature on the development of conservation (Piaget) in children in order to aid its use as a routine assessment instrument of an important aspect of cognitive development. The nature of conservation, a review of the literature, task variables, and training variables are discussed. The author concludes that performance on a conservation task is a reliable tool for specifying the level or stage at which the child is functioning; and that it is suitable for further research purposes (obtaining a rank ordering among subjects in a sample based on one facet of their cognitive ability.) Document EC 031 245 discusses the research project conducted. (CD)