Analogical reasoning is one mechanism that has been recognized as having the potential of bringing prior knowledge to bear on the acquisition of new information. Analogical reasoning involves the identification and transfer of structural information from a known system to a new and relatively unknown system. The productive use of analogy is often based on the recognition of some similarity in salient properties of the two systems, and not similarity in their structure, since the relevant structure of the target system is unknown. Examinations of analogical reasoning often ignore developmental questions of how children and adults acquire this mechanism, but such questions are crucial in terms of their impact on instruction. Analogical reasoning is available to children as well as adults. What develops is not the analogical mechanism itself but the conceptual system upon which this mechanism operates. (A table of data and a figure are included, and 63 references are attached.) (RS)