Piaget’s Stages of Cognitive Development as part of his theory have had a monumental impact on contemporary child developmental psychology.
Jean Piaget’s theory of Cognitive Development has had a monumental impact on contemporary developmental psychology. Despite challenges to his theory, his work remains a foundation for the modern understanding of child development.
However, Piaget’s theory and his stages of cognitive development are frequently misunderstood. It is best not to think of a child is “in” a stage at a particular moment in time, with parents anxiously testing their children to see if they are ahead or behind the ‘correct’ stage. The point is that there is a continual process of building cognitive abilities where later skills are built on earlier skills. Piaget first described the various forms of thinking used by children throughout childhood, but he was even more interested in the process of development through this sequence of stages, or forms of thinking. As a guide to what develops and how, his four cognitive development stages describe one part of his great legacy.
Part of the delight of Piaget’s work is his enormously insightful observations of children and his endless playful experimentation with them, including observing his own three children, about whom he wrote three ground-breaking books.
The process underlying Piaget’s stages of cognitive development
Piaget endorsed a view of the development of knowledge known as “constructivism”, according to which children come to understand the world through learning what they can do with it. He wrote that for children to learn about objects they “must act upon them and, therefore, transform them.” They come to learn about the world through learning to anticipate the potential to interact with objects and other people. Thus, perception, according to Piaget, is not just a passive process. To see a house is not just having an image enter one’s eye, but rather to understand it in terms of the potential to interact with it, that is, this object is a shelter one can enter.
Progress through the four stages of cognitive development that Piaget described made possible by a perpetual iterative process that results in movement toward more complete knowledge of the world.
As children develop knowledge, they learn activity patterns consisting of emotion, sensation, motor movement, and perception, learned in response to a particular interaction with the world (i.e., schemes). Once they develop a scheme within particular forms of interaction, children extend it to slightly different situations: “They cast the net of their schemes out into the world and what they catch depends on the structure of the net.” That is, what they perceive and understand about the world depends on their previously learned patterns of interaction, that is, in terms of potential for interaction.
Piaget describes two inter-linked processes through which knowledge develops:
Assimilation: The child understands new experience in terms of past experience (i.e., schemes). For example, when a baby sees a rattle she may assimilate it to her grasping scheme based on her past experience with objects that have a similar appearance, such as sticks. That is, she will understand this object in terms of her past experience, and so she will have expectations based on such previous encounters with sticks.
Accommodation: But because each new experience is somewhat different the child will accommodate to those differences and thus extend her knowledge in new ways. In this example, if the child picks up the rattle it may make a noise, unlike the sticks she has previously played with. Thus, new experiences change the child’s thinking fundamentally. She comes to think in a new way – that grasping this object may coincide with the rattling sound.
Piaget’s four stages of cognitive development
1. Sensorimotor (during the first two years)
This stage builds on action in the development of thinking during the first 18 months. Babies employ action schemes like sucking, pushing, hitting and grasping, in order to explore and manipulate the world. At the outset, the newborn has no self-consciousness and no clear awareness of what effects she produces. By coordinating her actions on objects in the context of other people, she develops a sense of her self and how she relates to people and things. Piaget described a series of 6 sub-stages within the sensorimotor stage.
Sub-stage 1: Reflex activity
During the first month, the baby sucks, roots, grasps, touches, cries, moves her arms and legs, and gets better at all of these actions. Piaget described these actions as reflexes but not in the sense of involuntary bodily movements. These are actions newborns engage in and they also improve these skills, such as sucking.
Sub-stage 2: Primary circular reactions
At this stage the baby’s activity focuses on his or her body (hence “primary”) and it is repetitive (hence “circular”) as the baby tries to re-create experiences, such as sucking a thumb. The baby is actively exploring.
Sub-stage 3: Secondary circular reactions
The baby starts to engage with objects and events (hence “secondary”). In the case of Piaget’s own daughter, repeated kicking in the cot made dolls that were hung up on the cot sway. The baby was not intending to make the doll sway, just enjoying that they did so and learning about the link between her kicking and the dolls moving. At this stage of development, babies are learning by accidental discovery. But it is focused on events in the world such as dolls moving rather than her experience based on her own body such as sucking.
Sub-stage 4: Coordination of secondary schemes
At this point, the baby starts to combine schemes to achieve a desired result – in the case of Piaget’s own child, an example involved pulling a string in order to get hold of a piece of paper attached to it. This demonstrates the emergence of intentional activity because the baby is doing one action in order to achieve something else.
Sub-stage 5: Tertiary circular reactions
At this stage the baby starts active experimentation. He or she can apply a scheme to achieve a result; if it does not work, the baby will try another scheme in his or her repertoire of action patterns.
Sub-stage 6: Invention of new means
Toddlers start to find new ways of doing things on their own initiative. In the case of Piaget’s own daughter, instead of backing away awkwardly after bumping a toy pram into a wall, she paused a moment and then walked round the pram in order to push it from the other side. It appeared that she was able to solve this problem by coordinating her actions implicitly or mentally without actually having to perform them.
This first stage comes to an end when the baby develops the ability to think through problems without actually having to test the solution out physically.
2. Pre-operational (between 2 and 7 years)
This stage starts with “pre-conceptual thought” which includes pretend play, drawing, using simple language and imitating actions even when they are not present and visible. A child at this stage does not distinguish between individual objects and the category they belong to. In the case of Piaget’s own daughter, she referred to every slug as “the slug”, that is, the very one that they had seen further back along the path.
Then comes the “intuition” sub-stage. The child starts to combine schemes in order to infer outcomes. The classical experiment is having two identical glasses of water with the same amount of water in each, then pouring one glass into a narrower glass, so the water is higher. The child, operating by focusing on only one dimension, deduces on the basis of existing schemes that a higher water level means more water in the tall thin glass, or that there is more water in the short glass because it is wider.
3. Concrete operational (7-11 years)
At this stage, the child understands the principle of conservation, that is, even though there can be a change in appearance, some underlying properties can remain the same. For example, in the experiment described above, there must be the same amount of water in each glass, because none was added or taken away, or because even though a glass was taller it was also narrower, and so changes in the two dimensions compensate for each other. A child will group, count and measure objects at this stage.
4. Formal operational (12-15 years)
At this stage children and adolescents can now experiment through forming hypotheses and systematically testing them out by trying out a series of alternatives, just like scientists. Piaget recognised that not everyone expresses skills at this stage as if they were scientists in a laboratory. He thought, however, that every adult may reach this stage in their own area of expertise in which they can systematically work through a problem in terms of the possible variables involved – farmers, bakers, mechanics and so on.
Criticisms of the Piaget stages of cognitive development
The criticisms of Piaget’s four stages of cognitive development tend to focus on misunderstandings or non-essential features that do not undermine the central tenets of his theory. Some have claimed his experiments were too difficult for children. But changing the procedure so that younger children can pass the tasks can result in testing different abilities. Others have criticised the ages associated with the stages and have pointed to diversity among children. Again, for Piaget, it was the sequence that was important, not the precise age at which a child reaches a particular point.
Another criticism is that children are inconsistent in each stage and use particular forms of thinking when working on specific tasks. That is, a child may not always use concrete operational thinking on all such tasks (referred to as “horizontal decalage”). This was thought to contradict Piaget’s theory, but it does so only if children are assumed to be in a stage. In fact, Piaget observed and predicted this result. It is expected on the basis of a full understanding of his theory, according to which children develop forms of thinking based on their experience. Therefore, whether or not a child will use concrete operational thinking will depend on if they have sufficient experience with the particular materials in a specific task.
Piaget’s theory of cognitive development has also been criticised for underestimating the importance of social factors in development. He is sometimes contrasted with Vygotsky, who so strongly emphasised the role of social interaction in development. But, ironically, Vygotsky actually criticised Piaget’s early work for being too focused on social factors! Piaget did recognize that social factors were clearly important and necessary in development, but that they alone did not fully explain development. He argued that what is also needed is the gradual back and forth process he described as equilibration.
The bottom line is that the Piaget theory of cognitive development remains an important foundation of modern developmental psychology. Further discoveries are serving to confirm the central thrust of his argument rather than to challenge it.
 p 704, Piaget J (1970). Piaget’s theory. In PH Mussen (ed), Carmichael’s Manual of Child Psychology (3rd ed, vol 1). New York: Wiley.
 p 40, Carpendale J, Lewis C & Muller U (2018), see below.