Describes an empirical method of developing learning hierarchies by comparing success on each tested behavior with all other behaviors. Advantages, compared with validation of a particular logical hierarchy, are illustrated by application of density principles to prediction of flotation. (AL)

Examines the transition from concrete to formal thought in Piagetian theory. The questions investigated relate to the abruptness of the transition period, the simultaneity of changes across schemes, and the influence of one scheme of development on another. (SA)