Stage theory of cognitive development (also known as developmental stage theory or genetic epistemology) was introduced by Swiss child psychologist Jean Piaget in the 1950s. This theory describes development of cognitive processes which are key to understanding, but also constrains of learning. According to Piaget,

• “Learning is no more than a sector of cognitive development that is facilitated by experience.”¹⁾

In 1947²⁾ Piaget has first introduced his four stages of human cognitive development: sensorimotor, preoperational, concrete, and formal, as they are described below. Ages describing when which stage occurs are the average values.

• Sensorimotor period (birth to 2 years): In this stage cognitive system of an infant is limited to motor reflexes, but also some more complex procedures built on those reflexes. Infant interacts with the environment, learns to understand the world and is acquiring the capacity for internalized thinking. Learning takes place through absorbing into the existing schema and accommodating when schema change is required.
• Preoperational period (2 to 7 years): Children now develop language and mental imagery skills, but still cannot conceptualize abstractly and don't have sense of time. Intelligence becomes less egocentric and more socialized. A child can now think about events and things that aren't present in the moment of speaking. He can see the world only from his perspective and assumes other do so as well. Teaching a child in this stage must take into account his not fully understand concepts of time phenomenon.
• Concrete-operational period (7 to 11 years): Children in this stage of development are able to analyze more perspectives simultaneously. Much of learning if performed through assimilation. Although they can understand concrete problems and develop reasoning skills, according to Piaget they still cannot analyze abstract problems and all of their logical consequences.
• Formal-operational period (11 to adolescence) : Piaget claims that the final form of cognition is reached in this stage. Abstract thinking capabilities in this stage are very similar to ones of adults. Individual at this stage is also capable of hypothetical and deductive but also reflective and analytical reasoning skills. This is supposed to be the final stage of cognitive development and although the knowledge base of an individual is still to be expanded, his thinking capabilities are now as strong as they would get.

³⁾

The importance of the Piaget's stage model are the constrains that stage of cognitive development sets on learning. These constrains mean that what can be learned depends on the current developmental stage. One should be taught to apply developed cognitive structures to new material, but to learn new strategies first the related cognitive structure has to evolve.

Piaget's theory suggests that in order to make learning effective, learner's stage of the cognitive development needs to be taken into account. General suggestions for adopting teaching methods to the four stages of development are following:

• Sensorimotor stage - teaching an infant in this stage should be orientated on its sensorimotor system.
• Preoperational stage - children can now actively engage in learning and exploring.
• Preoperational stage - learning in this stage is facilitated through an opportunity to ask questions and get explanations which allow learner to mentally manipulate information.
• Formal operations - teaching the adolescent expands in its dimensions as he is able to consider many possibilities from several perspectives.

Piaget's theory also suggests that teachers should

• value child's cognitive processes which led him to a conclusion as well as the conclusion,
• encourage him to learn with his peers
• encourage him to learn for himself, but always
• respect his current stage in cognitive development and not make forced steps forward.

What should also be taken into consideration is that although all children go through the same steps during their development, that do it at different rates. Educational process should therefore be more focused on individuals and small groups within a class than to the class as a whole unit.

One of the criticisms of Piaget's theory lies on the fact that nor him or coworkers didn't leave an instrument for diagnosing child's current stage of cognitive development.

Still, as a border between preoperational period and operational period Piaget suggested conservation experiments. For example, two equal glasses filled with liquid are presented to a child, after which liquid out of one glass is poured into a third, more narrow glass. The child is then asked which glass holds more liquid. Only a child in the concrete- or formal-operational period should realize both glasses hold equal amount of liquid.

According to Piaget's theory, the crossing between the stages cannot be overcome with any training, yet a number of experiments⁴⁾

Various criticisms of Piaget's work include:

• Oversimplification of stages/underestimating abilities of children - it has been shown that in some cases children can learn some concepts even before reaching a particular stage. Piaget's stages are therefore not as distinct as he assumed.
• Unscientific method - Piaget based his conclusions on observations of a rather small number of children who do not necessarily form a statistically representative sample.

It is often considered that Piaget's experiments weren't designed carefully enough to exclude other explanations, that he offered to little evidence for his theory and that he didn't address important questions like social and motivational influences on cognitive development.

• Sensorimotor stage, preoperational stage, preoperational stage, formal operations, cognitive development
• Jean Piaget

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