Mastery of the principle of conservation is an important milestone in the childs cognitive development.
Mastery of the principle of conservation is an important milestone in the child's cognitive development. Piaget believed that an important characteristic of concretely operational reasoning is the recognition that properties such as mass, volume, and liquid remain the same despite changes in the form of objects. These clips show two children, a 5-year-old and a 7-year-old, responding to Piaget's classic conservation-of-liquid task. In the first segment (top video), the experimenter pours an equal amount of liquid into two identical containers as the child watches. The 5-year-old correctly observes that both containers hold the same amount of liquid even when they are moved about the table. Then, the experiment pours the liquid from one container into a shorter, wider bowl, again as the child looks. This time, when questioned, the child mistakenly indicates that the bowl holds less. When asked why, the child simply responds that, "a big cup is shorter than a tall cup." In the second segment (bottom video), the 7-year-old confronts the same task. The older child is not fooled by the bowl's shape. Clearly for him, the amount of liquid is "conserved" even though its shape has changed. Moreover, he correctly expresses this principle to the experimenter. Mastery of the conservation principle is one of the important differences between children at the preoperational versus the concrete operational stage of cognitive development.