1. Piaget's Stage Theory of Development
Piaget was among other things, a psychologist who was interested in cognitive development.
After observation of many children, he posited that children progress through 4 stages and
that they all do so in the same order. These four stages are described below.
The Sensorimotor Period (birth to 2 years)
During this time, Piaget said that a child's cognitive system is limited to motor reflexes at
birth, but the child builds on these reflexes to develop more sophisicated procedures. They
learn to generalize their activities to a wider range of situations and coordinate them into
increasingly lengthy chains of behaviour.
PreOperational Thought (2 to 6 or 7 years)
At this age, according to Piaget, children acquire representational skills in the areas mental
imagery, and especially language. They are very self-oriented, and have an egocentric view;
that is, preoperational chldren can use these representational skills only to view the world
from their own perspective.
Concrete Operations (6/7 to 11/12)
As opposed to Preoperational children, children in the concrete operations stage are able to
take another's point of view and take into account more than one perspective simultaneously.
They can also represent transformations as well as static situations. Although they can
understand concrete problems, Piaget would argue that they cannot yet perform on abstract
problems, and that they do not consider all of the logically possible outcomes.
Formal Operations (11/12 to adult)
Children who attain the formal operation stage are capable of thinking logically and
abstractly. They can also reason theoretically. Piaget considered this the ultimate stage of
development, and stated that although the children would still have to revise their knowledge
base, their way of thinking was as powerful as it would get.
It is now thought that not every child reaches the formal operation stage. Developmental
psychologists also debate whether children do go through the stages in the way that Piaget
postulated. Whether Piaget was correct or not, however, it is safe to say that this theory of
cognitive development has had a tremendous influence on all modern developmental
psychologists.
Santrock, J. W. (1995). Children. Dubuque, IA: Brown & Benchmark.
Siegler, R. (1991). Children's Thinking. Englewood Cliffs, NJ: Prentice-Hall.

2. Vasta, R., Haith, M. M., & Miller, S. A. (1995). Child Psychology: The Modern Science.
New York, NY: Wiley.
Jean Piaget (1896-1980) was a biologist who originally studied molluscs (publishing twenty
scientific papers on them by the time he was 21) but moved into the study of the development
of children's understanding, through observing them and talking and listening to them while
they worked on exercises he set.
"Piaget's work on children's intellectual development owed much to his early studies of water snails"
(Satterly, 1987:622)
His view of how children's minds work and develop has been enormously influential,
particularly in educational theory. His particular insight was the role of maturation (simply
growing up) in children's increasing capacity to understand their world: they cannot
undertake certain tasks until they are psychologically mature enough to do so. His research
has spawned a great deal more, much of which has undermined the detail of his own, but like
many other original investigators, his importance comes from his overall vision.
He proposed that children's thinking does not develop entirely smoothly: instead, there are
certain points at which it "takes off" and moves into completely new areas and capabilities.
He saw these transitions as taking place at about 18 months, 7 years and 11 or 12 years. This
has been taken to mean that before these ages children are not capable (no matter how bright)
of understanding things in certain ways, and has been used as the basis for scheduling the
school curriculum. Whether or not should be the case is a different matter.
More
Piaget's Key Ideas
Adaptation What it says: adapting to the world through assimilation and accommodation
Assimilation The process by which a person takes material into their mind from the
environment, which may mean changing the evidence of their senses to make it
fit.
Accommodation The difference made to one's mind or concepts by the process of assimilation.
Note that assimilation and accommodation go together: you can't have one
without the other.
Classification The ability to group objects together on the basis of common features.
Class Inclusion The understanding, more advanced than simple classification, that some classes
or sets of objects are also sub-sets of a larger class. (E.g. there is a class of
objects called dogs. There is also a class called animals. But all dogs are also

3. animals, so the class of animals includes that of dogs)
Conservation The realisation that objects or sets of objects stay the same even when they are
changed about or made to look different.
Decentration The ability to move away from one system of classification to another one
as appropriate.
Egocentrism The belief that you are the centre of the universe and everything revolves
around you: the corresponding inability to see the world as someone else does
and adapt to it. Not moral "selfishness", just an early stage of psychological
development.
Operation The process of working something out in your head. Young children (in the
sensorimotor and pre-operational stages) have to act, and try things out in the
real world, to work things out (like count on fingers): older children and adults
can do more in their heads.
Schema (or
scheme)
The representation in the mind of a set of perceptions, ideas, and/or actions,
which go together.
Stage A period in a child's development in which he or she is capable of understanding
some things but not others
Stages of Cognitive Development
Stage Characterised by
Sensori-motor
(Birth-2 yrs)
Differentiates self from objects
Recognises self as agent of action and begins to act intentionally: e.g. pulls a
string to set mobile in motion or shakes a rattle to make a noise
Achieves object permanence: realises that things continue to exist even when no
longer present to the sense (pace Bishop Berkeley)
Pre-operational
(2-7 years)
Learns to use language and to represent objects by images and words
Thinking is still egocentric: has difficulty taking the viewpoint of others
Classifies objects by a single feature: e.g. groups together all the red blocks
regardless of shape or all the square blocks regardless of colour
Concrete operational Can think logically about objects and events

4. (7-11 years) Achieves conservation of number (age 6), mass (age 7), and weight (age 9)
Classifies objects according to several features and can order them in series
along a single dimension such as size.
Formal operational
(11 years and up)
Can think logically about abstract propositions and test hypotheses
systemtically
Becomes concerned with the hypothetical, the future, and ideological problems
The accumulating evidence is that this scheme is too rigid: many children manage concrete
operations earlier than he thought, and some people never attain formal operations (or at least
are not called upon to use them).
Piaget's approach is central to the school of cognitive theory known as "cognitive
constructivism": other scholars, known as "social constructivists", such as Vygotsky and
Bruner, have laid more emphasis on the part played by language and other people in enabling
children to learn.
See here for Howard Gardner's re-evaluation of Piaget: still a giant, but wrong in practically
every detail.
And the combination of neuroscience and evolutionary psychology is beginning to suggest
that the overall developmental model is based on dubious premises. (It's too early to give
authoritative references for this angle.)
Jean Piaget's Background
Jean Piaget was born in Switzerland in 1896. After receiving his doctoral degree at age 22,
Piaget formally began a career that would have a profound impact on both psychology and
education. After working with Alfred Binet, Piaget developed an interest in the intellectual
development of children. Based upon his observations, he concluded that children were not
less intelligent than adults, they simply think differently. Albert Einstein called Piaget's
discovery "so simple only a genius could have thought of it."
Piaget's stage theory describes the cognitive development of children. Cognitive development
involves changes in cognitive process and abilities. In Piaget's view, early cognitive
development involves processes based upon actions and later progresses into changes in
mental operations.
Key Concepts
Schemas - A schema describes both the mental and physical actions involved in
understanding and knowing. Schemas are categories of knowledge that help us to interpret
and understand the world.
In Piaget's view, a schema includes both a category of knowledge and the process of
obtaining that knowledge. As experiences happen, this new information is used to modify,
add to, or change previously existing schemas.

5. For example, a child may have a schema about a type of animal, such as a dog. If the child's
sole experience has been with small dogs, a child might believe that all dogs are small, furry,
and have four legs. Suppose then that the child encounters a very large dog. The child will
take in this new information, modifying the previously existing schema to include this new
information.
Assimilation - The process of taking in new information into our previously existing
schema's is known as assimilation. The process is somewhat subjective, because we tend to
modify experience or information somewhat to fit in with our preexisting beliefs. In the
example above, seeing a dog and labeling it "dog" is an example of assimilating the animal
into the child's dog schema.
Accommodation - Another part of adaptation involves changing or altering our existing
schemas in light of new information, a process known as accommodation. Accommodation
involves altering existing schemas, or ideas, as a result of new information or new
experiences. New schemas may also be developed during this process.
Equilibration - Piaget believed that all children try to strike a balance between assimilation
and accommodation, which is achieved through a mechanism Piaget called equilibration. As
children progress through the stages of cognitive development, it is important to maintain a
balance between applying previous knowledge (assimilation) and changing behavior to
account for new knowledge (accommodation). Equilibration helps explain how children are
able to move from one stage of thought into the next.
More About Piaget's Stages of Cognitive Development
The Sensorimotor Stage
The Preoperational Stage
The Concrete Operational Stage
The Formal Operational Stage
Support and Criticism of Piaget
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References
Santrock, John W. (2008). A topical approach to life-span development (4 ed.). New York City: McGraw-Hill.
Piaget, J. (1977). Gruber, H.E.; Voneche, J.J. eds. The essential Piaget. New York: Basic Books.
Piaget, J. (1983). Piaget's theory. In P. Mussen (ed). Handbook of Child Psychology. 4th edition. Vol. 1. New York: Wiley.

6. More About Cognitive Development
Biography of Jean Piaget
Sensorimotor Stage of Cognitive Development
Preoperational Stage of Cognitive Development
More About Cognitive Development
Concrete Operational Stage of Cognitive Development
Formal Operational Stage of Cognitive Development
Cognitive Development in Early Childhood
Suggested Reading
Quiz - Piaget's Stages of Cognitive Development
Support and Criticism of Piaget's Stage Theory
Kohlberg's Theory of Moral Development