Cognitive Development: Piaget

One of the questions you may be asked on Paper II is to "Evaluate two theories of cognitive development." One of the most influential theories in the study of development is Piaget's stages of cognitive development.

When answering this question, please be sure not to spend a lot of time outlining all four stages and their sub-stages! The focus of the response should be on the evaluation of the theory and not a lot of detail about the theory itself. Of course, you do have to demonstrate some basic knowledge of the theory in order to earn high marks in content.

Description of the theory

Piaget believed that children are “active scientists” who learn by interacting with their social and physical environment.  He also argued that cognitive development is the result of biological maturation. Piaget believed that the process of thinking and the intellectual development could be regarded as an extension of the biological process of the evolutionary adaptation of the species.

Piaget proposed a stage theory that is universal in nature. All of us pass through the stages in the same order.  You do not need to be able to outline the stages in detail in order to answer the relevant essay on Paper II, but it is important for you to have an overall sense of the four stages.

  • Stage 1: The sensorimotor stage (birth to 2 years old). Children experience the world through movement and their five senses. They achieve object permanence at 8 months.
  • Stage 2: Preoperational stage (age 2 to 7). Characterized by egocentrism, the inability to differentiate between fantasy & reality (magical thinking) and the inability to understand conservation.
  • Stage 3: Concrete operational stage (7 - 11). Begin to use logic, but need concrete objects to manipulate. An age for gathering a lot of information. No longer egocentric, but able to understand other points of view.
  • Stage 4: Formal operational stage (age 12 and up) Can think abstractly.

Here is a film that expands a bit more on Piaget's theory

Support for Piaget's theory of cognitive development

Piaget & Inhelder (1956) - the three-mountain task

In this study, children were shown a three-dimensional display of a mountain scene. They were then asked to choose a picture that showed the scene they had observed. In general, the children were able to do this with little difficulty. However, when four-year-olds were asked to select a picture showing what a doll sitting across the table would have observed when looking at the mountain, they chose the same image - reflecting their own viewpoint. Piaget used this to show the egocentrism of children - that is, their inability to see another person's perspective.  By the time children reached the age of seven, they were able to do this task with little problem.

Li et al. (1999) tested Chinese primary school children. They found support for Piaget’s research on the liquid conservation task. However, they also found that students who were schooled developed this ability sooner than unschooled children.  This shows that the stages may not be as fixed with regard to the age of the child as Piaget believed.  Schooling appears to have an effect on the rate of a child's cognitive development.

Piaget's own research has proven to be highly reliable.  For example, the film below demonstrates children's understanding of the concept of conservation. As with Li et al's study above, we can see that there is a stage when children are not able to understand this concept and then a point in time where this is a basic understanding.  This appears to indicate that children develop over time.

And a film on symbolic understandings and scale

Finally, Piaget's theories have been applied successfully in education.  Today the idea of teaching children "developmentally appropriate" skills is a fundamental part of teacher education.  Understanding which skills children can do at which age, as well as understanding that skills can be scaffolded over time, are important applications of Piagetian theory.

Challenges to Piaget's Theory of Cognitive Development

Hughes (1975) argued that the three mountains task did not make sense to children.  It was made more difficult by asking the children to think about what the doll saw and to match it to a set of photographs. He wanted to created a task that would be more "age appropriate." He showed children a model comprising two intersecting walls (see image to the left).  The researcher then placed a policeman doll at one of the points on the "X." The children were asked to place another doll - a "boy doll" - somewhere in the walls so that the policeman couldn't see him. The four-year-olds had no problems with this task.

Then Hughes introduced a second policeman doll and placed both dolls at the ends of two walls (see image to the left). The child was then asked to once again hide the boy doll from the policemen.  This would require the child to consider two points of view. 90 percent of children age 3.5 to 5 years old were able to do this task without error.

When he added more walls and a third policeman, 90 percent of four-year-olds were still able to do the task without any difficulty. Hughes showed that by four years old children have lost their egocentric thinking. So, he didn't argue that the stages do not exist, but that Piaget overestimated how long it took for this skill to develop.

Baillargeon & De Vos used the fixed gaze of an infant in order to determine whether they have established “object permanence.” Her findings in her “impossible situation test” have indicated that babies obtain object permanence earlier than Piaget had claimed.  See the video clip below for an explanation of their research.



  • The first theory of its kind. His theory that cognitive changes are driven by biological maturation is widely accepted and supported.
  • Research consistently supports the progression of cognitive development as outlined by Piaget.
  • Piaget saw children as active learners rather than passive processors.
  • Piaget has had a major effect on education.
  • The theory has cross-cultural support.


  • Sampling bias.  Piaget's original research was on his own children.  He then went on to study other children, but they were children of well-educated professionals of high socioeconomic status. The original sample was not representative and thus it is difficult to generalize the findings.
  • The original studies used tasks that were too language dependent and were not age-appropriate for the children.
  • Piaget over-estimated people’s formal operational ability. Around one-third of the population reaches this stage later in life, or not at all.
  • The theory is descriptive rather than explanatory.
  • As seen in later research, the ages at which the stages begin has been criticized. Evidence shows that often children enter the stages earlier than Piaget predicted.
  • Post Piagetian theorists have argued that formal operations is not a sufficient description of a lot of adult thinking. They have proposed “Post-formal thinking” which involves being able to tolerate ambiguity and to avoid dichotomous thinking patterns. Post-formal thinking also is able to take the situation into account when making decisions and understands the role of emotion in decision making. This type of thinking which interacts with the environmental constraints and individual emotion and looks at the range of possibilities, is much more sophisticated than the simple description of “abstract thinking” proposed by Piaget.
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