The concrete operations stage begins at age six or seven, when the schoolage
child becomes capable of keeping in mind and logically manipulating
several concrete objects at the same time. The child is no longer the prisoner
of the momentary appearance of things. In no case is the change more
evident than in the sort of problem in which a number of objects (such as
twelve black checkers) are spread out into four groups of three. While the
four-year-old, preoperational child would be likely to say that now there are
more checkers because they take up a larger area, to the eight-year-old it is
obvious that this transformation could easily be reversed by regrouping the
checkers. Piaget describes the capacity to visualize the reversibility of such
transformations as “conservation.” This understanding is fundamental to
the comprehension of simple arithmetical manipulations. It is also fundamental
to a second operational skill: categorization. To the concreteoperational
child, it seems obvious that while Rover the dog can for other
purposes be classified as a household pet, an animal, or a living organism, it
will still be a “dog” and still be “Rover.” A related skill is seriation: keeping in
mind that an entire series of objects can be arranged along a single dimension,
such as size (from smallest to largest). The child now is also capable
of role-taking, of understanding the different perspective of a parent or
teacher. No longer egocentric (assuming that everyone shares one’s own
perspective and cognitively unable to understand the different perspective
of another), the child becomes able to see himself or herself as others see
him or her and to temper the harshness of absolute rules with a comprehension
of the viewpoints of others.