Stage theories are based on the idea that elements in systems move through a pattern of distinct stages over time and that these stages can be described based on their distinguishing characteristics. Specifically, stages in cognitive development have a constant order of succession, later stages integrate the achievements of earlier stages, and each is characterized by a particular type of structure of mental processes which is specific to it. The time of appearance may vary to a certain extent depending upon environmental conditions.

"Stage theory" can also be applied beyond psychology to describe phenomena more generally where multiple phases lead to an outcome. The term "stage theory" can thus be applied to various scientific, sociological and business disciplines. In these contexts, stages may not be as rigidly defined, and it is possible for individuals within the multi-stage process to revert to earlier stages or skip some stages entirely.

Piaget's theory of cognitive development

Piaget

Jean Piaget

Jean Piaget was a French-speaking Swiss developmental psychologist and philosopher known for his epistemological studies with children. His theory of cognitive development and epistemological view are together called "genetic epistemology"....

's theory goes through four stages: Sensorimotor: (birth to 2 years), Preoperations: (2 to 7 years), Concrete operations: (7 to 11 years), and Formal Operations: (11 to 16 years). Each stage has at least two substages, usually called early and fully. Also see Theory of cognitive development

Theory of cognitive development

Piaget's theory of cognitive development is a comprehensive theory about the nature and development of human intelligence first developed by Jean Piaget. It is primarily known as a developmental stage theory, but in fact, it deals with the nature of knowledge itself and how humans come gradually to...

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Underlying Assumptions

• Each stage lays the foundation for the next.
• Everyone goes through the stages in the same order.
• Each stage is qualitatively different. Meaning it is a change in nature, not just quantity
• The child is an active learner. Basically they have to do it on their own, they cannot be told.

Sensorimotor Stage (birth to 2 years)

A child comes into the world knowing almost nothing, but they have the potential that comes in the form of:

• brain makeup
• reflexes eg. sucking and visual orienting
• innate tendencies to adapt to environment

Infants use these potentials to explore and gain an understanding about themselves and the environment. They have a lack of object permanence, which means they have little or no ability to conceive things as existing outside their immediate vicinity. For example: when you place a barrier, such as a piece of wood, in front of an object an infant will believe that the object is nonexistent.

Preoperational Stage (2 to 7 years)

Preoperational intelligence means the young child is capable of mental representations, but does not have a system for organising this thinking (intuitive rather than logical thought).
The child is egocentric – which is they have problems distinguishing from their own perceptions and perceptions of others.
A classic example is, a preoperational child will cover their eyes so they can not see someone and think that that person can not see them either.

The child also has rigid thinking, which involves the following:

• Centration – a child will become completely fixed on one point, not allowing them to see the wider picture. For example, focusing only on the height of the container rather than both the height and width when determining what has the biggest volume.
• State – can only concentrate on what something looks like at that time.
• Appearance – focuses on how something appears rather than reality.
• Lack of Reversibility – can not reverse the steps they have taken. Does not realize that one set of steps can be cancelled by another set of steps.
• Lack of Conservation – realizing that something can have the same properties even if it appears differently.

Concrete Operations (7 to 11 years)

• Intelligence is now both symbolic and logical.
• Acquires ‘operations’ = a set of general rules and strategies.
• The most critical part of operations is realising ‘reversibility’ = both physical and mental processes can be reversed and cancelled out by others.

The concrete operational child will overcome the aspects of rigidity apparent in a preoperational child. These are:

• lack of reversibility
• states
• appearance
• conservation

The tasks of concrete operations are:

• Seriation – putting items (such as toys) in height order.
• Classification – the difference between two similar items such as daisies and roses.
• Conservation – realising something can have same properties, even if it appears differently.

It is important to realise that operations and conservations do not develop at the same time. They develop gradually and are not an ‘all or nothing’ phenomenon. For example, the first to develop is number conservation followed by mass conservation, area conservation, liquid conservation and finally solid volume conservation.
Thinking is not abstract. It is limited to concrete phenomena and the child’s own past experiences.

Formal operations (11 to 16 years)

• Child is capable of formulating hypotheses and then testing them against reality.
• Thinking is abstract, that is a child/adolescent can formulate all the possible outcomes before beginning the problem. They are also capable of deductive reasoning.

Neo-Piagetian and Post-Piagetian Stage Theories

Juan Pascaual-Leone was the first to propose a neoPiagetian stage theory. Since that time there have been several neo-Piagetian theories of cognitive development

Neo-Piagetian theories of cognitive development

Jean Piaget's theory of cognitive development has been criticized on many grounds. One criticism is concerned with the very nature of development itself. It is suggested that Piaget's theory does not explain why development from stage to stage occurs. The theory is also criticized for ignoring...

. Only the ones that cover at least infancy through adulthood are mentioned here. These include the theories of Robbie Case, Grame Halford, Andreas Demetriou

Andreas Demetriou

Andreas Demetriou is a well known Greek Cypriot developmental psychologist and a former Minister of Education and Culture of Cyprus.- Life :...

 and Kurt W. Fischer. The theory of Michael Commons

Michael Commons

Michael Lamport Commons is a theoretical behavioral scientist and a complex systems scientist. He developed the Model of Hierarchical Complexity...

 and Francis Asbury Richards' Model of Hierarchical Complexity

Model of hierarchical complexity

The model of hierarchical complexity is a framework for scoring how complex a behavior is. It quantifies the order of hierarchical complexity of a task based on mathematical principles of how the information is organized and of information science...

is also relevant. The description of stages in these theories is more elaborate and focuses on underlying mechanisms of information processing rather than on reasoning as such. In fact, development in information processing capacity is invoked to explain the development of reasoning. More stages are described (as many as 15 stages), with 4 being added beyond the stage of Formal operations. Most stage sequences map onto one another. PostPiagetian stages are free of content and context and are therefore very powerful and general.