Investigated was the distinction between identity conservation and equivalence conservation in 180 preschool, kindergarten and third grade students. Ss were assigned to one of six different counterbalanced orders of presentation for the conservation task battery. The factors were age, task (identity/equivalence), criterion (judgment only/judgment plus explanation), and content area (length/weight). Among results were greater difficulty indicated for equivalence than identity conservation and significant performance improvement at every grade level for the transitivity tasks. (CL)