ABSTRACT
The possibility of solving the inclusion problem is, therefore, according to Piaget, the central experience for the situation of equilibrium that must be achieved with respect to Grouping I. The inclusion problem seemed to be still more difficult with the pictures of animals. Albert Morf carried out a first leaning experiment by helping children of four to seven years of age to discover the solution to the inclusion problems. One of David Elkind's intentions in his Piaget Replication Study III was "to determine whether Piaget's stages were significantly related to age." Jan Smedslund used the problem of class inclusion as the first item in a series of 9 Piaget problems given to 160 children in Boulder, Colorado. The only criterion adopted for the criterion "spontaneous insight in inclusion problems" was the giving of good answers–thus without justifications.
