A model of conceptual learning and development that provides a framework for studying the course of cognitive development throughout the school years and also studying the learning concepts across short time intervals is discussed in this paper. The theory includes five main propositions. First, children learn four successively higher levels of the same concept in an invariant sequence. The four levels are designated concrete, identity, classificatory, and formal. The rates at which individuals attain the successive levels vary and not all individuals attain the formal level of many concepts. Also, the age at which the individual attains a certain level varies among concepts. Results of factor analytic studies examining the relationship between the structure of cognitive and educational development are presented. The present set of studies indicates that scales can be constructed to measure the course of cognitive development, based directly on a theory that specifies the mental operations required to attain successive levels of the same concept and also the uses that individuals can make of the concepts they have learned. (Author/AM)