Cross-sectional studies have shown that children acquire the con cept of conservation of discontinuous quantities (when the experi mental material consists of small collections of objects) between six months to one year earlier than that of continuous quantities. This raises the question, which in fact constitutes one of the major con cerns of the learning studies, of the relationships between the two concepts. Does one concept stem directly from the other? Or are they both products of the same process of elaboration applied to a different content? How does the child progress from one concept to the other?