Johnny is a 4-year-old who is having lunch with his mother and sister. When his mother pours the milk that is left in the carton into the children's glasses, she finds that there is not enough to fill both glasses; so she carefully pours half of the milk in the shorter, fatter glass in front of Johnny and half into a thin, taller glass in front of Johnny's sister. Immediately, Johnny complains that his sister got more milk than he did, and even when his mother tries to explain that they both got the same amount, Johnny insists he is right. In this example, Johnny is demonstrating a lack of development in the area of:

Conservation is the concept of cognitive development theory that is given by Jean Piaget. Conservation is related to the logical thinking ability results in the perception pf a person is the same for the adjustment of a container, size, and shape. The pre-operational stage of cognitive development theory lacks the conservation ability in children at the age of 2 to 7 years old. But later on the concrete stage, this ability develops in children. The children could not manipulate their intentionally their perception due to the lacking of conservation. The result is that they can be easily manipulated by their parents and elders. The children lack conservation that results in that children do not understand that the quantities do not change if the shape has been changed of the container.