Key points are not available for this paper at this time.
Peter B. Pufall, Robert E. Shaw, Ann Syrdal-Lasky, Development of Number Conservation: An Examination of Some Predictions from Piaget's Stage Analysis and Equilibration Model, Child Development, Vol. 44, No. 1 (Mar., 1973), pp. 21-27
Pufall et al. (Thu,) studied this question.