Swiss developmental psychologist Jean Piaget, who died in 1980 at the age of 84, is best known for his theory of child cognitive development. He believed that children develop knowledge in organized stages, each of which builds upon the earlier stages. His work was the foundation for skill-based school curricula. He categorized child development in four distinct stages, the first stage of which is divided into six sub-stages.
The first stage of child development occurs from birth to approximately two years. It is divided into six sub-stages which are each characterized by development of a new skill. The sub-stages are: reflexes; primary circular reactions; secondary circular reactions; coordination of reactions; tertiary circular reactions; and early representational thought. From birth to one month, the child understands the world through inborn reflexes such as looking and sucking. From one to four months, the child will coordinate sensations. From four to eight months, the the child becomes more focused and intentionally repeats actions to trigger responses. From eight to twelve months, the child will begin exploring the environment around him and imitate the observed behaviors of others. From twelve to eighteen months, the child will start trial and error experimentation, trying out different sounds and actions to get attention. From eighteen months to two years, the child will start to understand the world through mental cognition as opposed to purely actions.
Between two and six years, the development of language skills is predominant. It also becomes evident during this stage that a child is capable of implementing symbolism; she can use objects to symbolize others, such as using objects in play to represent other things, a broom for a horse or a box for a car.
Concrete Operational Stage
From age seven to around eleven, a child starts to develop skills in logical thinking, although deductive logic takes longer to develop. The child also begins to understand the reversibility of actions. For example, if he upsets someone, he realizes he can undo his action with an apology or action. He also starts to understand the relationships between categories; he understands that a ball is circular and that a circle is a shape. He understands that there are other shapes and the connection between them.
Formal Operational Stage
This stage starts at age 12 and continues until adulthood. During this time, a child develops his ability to think about abstract concepts. Logical thought, deductive logical reasoning and the ability to plan emerge during this stage. He can do mathematical calculations, think creatively and imagine the outcome of particular actions.