Stages of Development

Jean Piaget was among the first psychologists to wrestle with the question of how a child develops from simple-thinking newborn to cognitively sophisticated adolescent and adult. Over a lifetime of grappling with this question, he developed a theory of cognitive development in which he identified four major stages or "periods" of development. Underlying this theory are the ideas that each stage of development is a self-contained unit, that each builds upon the preceding stage, that each proceeds from a loosely defined unit into a tightly integrated model, and that children proceed through these stages in a universal, fixed order.

Piaget's stage model centers around the concept of schemas, that is, basic units of knowledge that serve as the building blocks of and framework for intellectual development. Infants in the first couple of years of life, according to Piaget, are capable only of forming simple schemas based on their actual physical encounters with the world: They must experience the world through their senses or motor actions (e.g., touch it, grab it, suck on it, bang it, throw it) in order to know anything about it. Piaget thus termed this the sensorimotor period of development. In the sensori-motor period, schemas are simple. For example, the very young infant develops a sucking schema; that is, the infant organizes information according to what can be sucked (fingers, pacifier, teething ring) and how sucking actions can vary (hard or soft, fast or slow). As the child grows and experiences new things in the world, schemas become more complex.

Perhaps the crowning achievement of the sensori-motor period is the development of the idea that things exist independent of the child, even when the object is out of sight. This amazing new ability is called object permanence. According to Piaget, this knowledge (reflected in the toddler's continued search for an object even after it has been hidden) reflects an ability on the part of the child to form a mental representation of the object and thus allows the child to be able to think about the object without having to experience it via the senses or motor activity.

The ability to form mental representations opens up a whole new world of learning and imagination for children in the preoperational period (roughly from age two to seven years). They engage in pretend play ("there's a monster coming; hide!"); they can role play ("I am the mommy, you are the baby"); they can imagine something even when nothing is there at all (for example, "eating" a seven-course meal off an empty toy dish); they can use one object to stand for another (for example, using a shoe box as a bus). Somewhere around age six or seven, according to Piaget, children enter the concrete operational period of development. Now they become capable of performing simple "mental operations" such as adding, sorting, or ordering objects. They are no longer bound by their own perceptions of things; rather, they recognize that others have their own perspectives and that objects have their own constant properties. Nevertheless, children's ability to perform these operations is limited to real, concrete objects and to the here and now. Once they can apply such operations to abstract concepts and possibilities (usually around age eleven or older), they are said to have reached Piaget's final stage, the formal operational period.

Piaget's theory of cognitive development is a perfect example of a stage theory of development. New information is being added as children grow and experience the world, but there are also qualitative shifts in the way that information is organized to help the child understand the world. Piaget's theory is still the springboard for much of the research on cognitive development that has taken place in the years since his death. Some of this later work, however, has shown that modifications must be made to the original theory.

First, it now seems that the characteristics of the stages that Piaget described are less consistent and less global than he had portrayed. As their ways of thinking mature, children will sometimes show more sophisticated ways of thinking in just one area, or with one type of task, or with one set of objects. For example, contrary to Piaget's belief, not all preoperational children are invariably egocentric (i.e., incapable of taking the perspective of others). Children's performances on some of the classic Piagetian tasks seem to be dependent in part on how familiar the children are with the objects, how well they understand the instructions, what experience they have with similar tasks, etc. Furthermore, it appears that some of Piaget's beliefs about young children's limited abilities may have arisen as a function of a limitation of his research methods. As researchers have uncovered increasingly clever and technologically advanced ways to tap the mental activity of young infants, they have found that even very young infants understand, remember, and can learn far more than Piaget ever realized. In summary, then, psychologists now think of cognitive development as proceeding in terms of gradual changes to higher levels of thinking rather than sudden advances from one style of thinking to another, more sophisticated style.