Piaget's Theory of Cognitive Development

Jean Piaget (1896–1980) is one of the most influential developmental psychologists. His theory proposes that children actively construct their understanding of the world through schemas, and that cognitive development proceeds through four universal stages. This lesson covers Piaget's key concepts, the four stages, research evidence, and critical evaluation.

Key Definition: A schema is a mental framework or "building block" of knowledge that helps an individual organise and interpret information. Schemas develop and become more complex through experience.

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Key Concepts

Schemas

Piaget argued that children are born with a small number of innate schemas (reflexes such as sucking, grasping). Through interaction with the environment, these simple schemas become elaborated and new schemas are formed.

Adaptation: Assimilation and Accommodation

Children adapt their schemas through two complementary processes:

Process	Definition	Example
Assimilation	Incorporating new information into an existing schema without changing the schema	A child who knows the schema "dog" (four legs, fur, tail) sees a new dog breed and assimilates it into the "dog" schema
Accommodation	Modifying an existing schema (or creating a new one) to fit new information that does not match	The same child sees a cat for the first time. It has four legs and fur, but is clearly not a dog. The child creates a new "cat" schema — this is accommodation

Equilibration

Key Definition: Equilibration is the driving force of cognitive development. It is the process of moving from a state of cognitive disequilibrium (when new information does not fit existing schemas) to equilibrium (when schemas adequately explain the world).

When a child encounters something that challenges their existing schemas, they experience disequilibrium — a state of cognitive discomfort. To restore equilibrium, the child must accommodate their schemas. This cycle of disequilibrium → accommodation → equilibrium drives development forward.

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Piaget's Four Stages of Cognitive Development

Piaget proposed that all children pass through four stages in the same order, with each stage characterised by qualitatively different ways of thinking:

graph LR
    A["Sensorimotor<br/>(0–2 years)"] --> B["Preoperational<br/>(2–7 years)"]
    B --> C["Concrete Operational<br/>(7–11 years)"]
    C --> D["Formal Operational<br/>(11+ years)"]

Stage 1: Sensorimotor (0–2 years)

The infant learns about the world through sensory experiences and motor actions (touching, looking, sucking, grasping).

Key development: Object permanence

Key Definition: Object permanence is the understanding that objects continue to exist even when they cannot be seen. Piaget argued that infants under approximately 8 months lack object permanence — when an object is hidden, they behave as if it no longer exists.

Piaget's evidence: Piaget observed that infants under about 8 months did not search for a toy that was hidden under a blanket, even if they had been reaching for it moments earlier. After 8 months, infants began to search for hidden objects, indicating the emergence of object permanence.

A-not-B error: Even after achieving object permanence, infants around 8–12 months make a characteristic error. If an object is hidden at location A several times, then moved to location B while the infant watches, the infant will still search at location A. Piaget interpreted this as evidence that the infant's schema for the object is tied to the action of reaching to A.

Stage 2: Preoperational (2–7 years)

The child can use symbolic thought (language, pretend play, drawing) but has several cognitive limitations:

Egocentrism: The inability to see the world from another person's perspective.

Piaget's evidence — The Three Mountains Task:

• Children were shown a model of three mountains of different sizes, colours, and features (snow, cross, hut).
• A doll was placed at a different position around the model.
• Children were asked to select a picture showing what the doll would see.
• Children under 7 consistently chose the picture matching their own viewpoint, not the doll's, indicating egocentrism.

Conservation: The understanding that quantity remains the same despite changes in appearance.

Piaget's conservation experiments:

• Number: Two equal rows of counters are shown. One row is spread out. Children under 7 say the longer row has "more" counters.
• Liquid: Equal amounts of liquid in identical glasses. One is poured into a taller, thinner glass. Children under 7 say the taller glass has "more."
• Mass: Two equal balls of clay. One is rolled into a sausage shape. Children under 7 say the sausage has "more."

Preoperational children fail conservation tasks because they focus on one dimension (height, length) rather than coordinating multiple dimensions — a tendency Piaget called centration.

Exam Tip: When describing conservation tasks, always specify the type (number, liquid, mass) and explain that the child focuses on appearance rather than underlying quantity. This demonstrates precise AO1 knowledge.

Stage 3: Concrete Operational (7–11 years)