Children's Perception of Conservation of Mass

This illustrates three tests of conservation. Most adults realize that a volume of water remains constant when poured into a taller, narrower container, even though the new level is higher. Early in the preoperational period, children fail to recognize this fact; they will say that the taller container has more water. The three tests shown here demonstrate that the ability to realize that objects retain mass, number, or length when they undergo transformation is acquired after the preoperational period.