In another example of conservation skills, a child is shown two identical glasses of liquid. When asked whether the two glasses contain the same amount of liquid, he will agree. As he watches, one glass of liquid is poured into a taller, thinner glass. The child now believes that the taller thinner glass contains more liquid. Conservation is the understanding that a given physical quantity does not change despite superficial changes in its appearance.
Preoperational children lack an understanding of conservation.
Lacks Reversibility Children in the preoperational stage of reasoning lack an understanding of reversibility. They do not understand that an action can be done and then undone. It is not until the age of 6 or 7 that children progress to the next stage of cognitive development, the concrete operational stage, when their thinking skills progress beyond these limitations. Children develop at their own pace. Challenge the child's abilities, but do not present material or information that is too far beyond his or her level.