Conservation performance during childhood to portions of the life span beyond adolescence is examined, with existing data replicated on subjects ranging from the preschool to middle-childhood years. Age differences in performance are studied for the typical Piagetian paired-stimulus equivalence conservation of number, substance, weight, and volume tasks in subjects ranging in age from 6 to 82 years. Results indicate that the performance apex for conservation ability attained after childhood may not be as stable an acquisition as Piaget's theory implies. Rather, a regression with age to less complex modes of responding is noted, at least for the more complex tasks in the battery. The ability to conserve number, hypothesized to be the earliest appearing and therefore the most simple concept, remained stable even in the oldest subjects. The concepts of intermediate difficulty (substance and weight conservation) were present in only about half the oldest group. The formal operation of volume conservation, regarded as the latest developing and most complex acquisition had virtually disappeared from the response repertoire of the oldest subjects. Further research with large numbers of older subjects is needed. (LH)