Piaget theorised that there were four stages of development in the thought processes of people. These stages were the sensorimotor period, the preoperational period, the concrete operational period and the formal operational period.


The sensorimotor period prevails from birth to two years of age and is divided into six substages. It is characterised by the absence of language and internal representation according to Le Francois (2000). The construction of knowledge begins with the childs ability to perform actions on the world through their senses and reflexes. As time passes, these actions become more deliberate, coordinated and planned. They become purposeful movements. This means that the child’s intelligence and knowledge about the world are limited to the actions they perform on their environment. They learn to solve reasonably complex problems without the help of mental representation. Over this stage there is a shift from the sensorimotor thinking base discussed above to representational thinking.

Learning takes place through adaption and Piaget believed that adaption had two aspects, assimilation and accommodation. Assimilation is the aspect that conserves the organisation of information and absorbs it into existing schema, and accommodation occurs when an object cannot be assimilated and the schemata have to be modified to include the object (Piaget, 1981). Schemata are our general knowledge bases about objects or events, acquired from past experiences (Matlin, 1998). Another characteristic of a child in the sensorimotor stage is the child’s inability to distinguish herself from the world surrounding her. Within this period the transition occurs from what Sigmund Freud called the “oceanic feeling” (inability to separate the self from the external world) to the ability to make the distinction between the two (Bjorklund, 1995). This is seen in the development of object permanance. Object permanace is the development of the knowledge that objects exist even when they cannot be percieved. A teddy bear hidden behind a screen is still in existence and is worth searching for, it has not suddenly disappeared off the face of the earth. Sensorimotor Development

Substage One: Basic Reflexes

(Birth – 1 month)

Children enter the world equipped with a set of inherited action patterns and reflexes through which they experience their environment. The intellectual development of the child begins through these actions as this is how the child acquires knowledge about its surroundings; this knowledge forms the basis for more complex developments further down the track. Infants are restricted in what they can know as their behaviours and schemata are limited. Adaption to their surroundings through assimilation and accommodation begins in this stage.

Substage Two: Primary Circular Reactions

(1 – 4 months)

In the second substage of Piaget’s theory, the knowledge and intelligence of the infant now extends beyond the innate behaviours they were born with but these new acquistions have only come about through the accommodation of schemata. The infants show one of the first signs learning which is modifying their reflexes as a result of their environment (Bjorklund, 1995). These acquistions come about by a circular means. Actions that are at first random and activate a reflex are attempted again to try and induce the experience again. The signs of intentionality have appeared. These patterns of learning have been labelled primary circular reactions.

This is also the substage in which object permanence begins to develop and the active search for a hidden object begins.

Substage Three: Secondary Circular Reactions

(4 – 8 months)

Secondary circular reactions are the first acquired adaptions of behaviours that are not reflexive, as opposed to the primary circular reactions which are reflex based. An infant in this stage may accidentally cause something interesting to happen and then seek to re-create the happy event. The interesting events in this case are located in the external wolrd, in primary circular reactions the interesting events are occuring within the body. A child in this substage, however, does still not understand the aspects of cause and effect and so will sift through the many behaviours it was indulging in when the event occurred and narrow it down to the particular action without really understanding the underlying concepts of why the event recurs.

Substage Four: Coordination of Secondary Circular Reactions

(8 – 12 months)

The actions of the previous stage flourish in this stage and continue to develop, the difference is that the need now precedes the act. Intentionality occurs in interactions with the environment and the infant is moving towards goal directed behaviour. An understanding of cause and effect relationships has come into being in the childs world.

Substage Five: Tertiary Circular Reactions

(12 – 18 months)

As with stage four, this stage is characterised by a means/ends differentiation. The infants are no longer restricted to the application of previously established schemata to obtain a goal. They can make the necessary alterations to their schemata to solve problems; this reflects a process of active experimentation (Bjorklund, 1995). These differences in cognition coincide with improved locomotive abilities; the children have become more physically active. In this stage, causal inferences are still unavailable to the infant; it must see an action occur before it has any understanding of the causal relationship.

Substage Six: Invention of new Means through Mental Combinations

(18 – 24 months)

The earlier stages of the sensorimotor period appear to be set on a continuum but the transition from the fifth to the sixth stage is more of a disjointed transition. Symbolic function and mental representation first appear during this stage, this runs parrallel with the development of language. Language is an expression of symbolic function and mental representation and it is at this stage that the children begin to string words together in pairs, the origins of sentences.


The preoperational period has been divided into two stages, the preconceptual stage and the intuitive stage. In the preconceptual stage of thinking, children have a certain understanding of class membership, and can divide their internal representations into classes, however, they cannot differentiate between members of the class, so if they see two different members of a class at different times, they believe them to be the same object. A famous example of this is seen in a story Piaget tells of his son who sees a snail and then a few metres along the footpath sees another snail and yet believes it to be the same snail (Le Francois, 2000). In this stage children think transductively as opposed to either deductively or inductively. The latter two refer to making generalisations from particulars and particulars from generalisations. Transductive thinking is inferring particulars from particulars, an example of this would be assuming a mouse was a rat because the mouse has a long scaly tail which fits into the childs rat schema, this is inferring a particular from a particular.

Intuitive thinking is a concept applicable to the last half of the preoperational stage, from 4 – 7 years. In this stage children are thinking more logically than they were before hand although the logic they follow is a little faulty. A good example of this is that the children in this period of development cannot yet conserve. There ideas relating to class membership are also blossoming quite well, however, they have trouble understanding that classes can themselves belong to a bigger organisation. If given a picture of oranges and apples in which there were 7 apples and only 3 oranges, they preoperational child in the second stage will say that there are more apples than there are pieces of fruit, even though this number equals 10.

Aside from all of this, one of the major achievements of the preoperational child is the use of symbols and language. The achievement of representation can be seen in deferred imitation, symbolic play and spoken language. Language helps the children to internalise their behaviours through representation which accelerates experiences as actions do not need to be physically performed, children can imagine the outcomes of their actions (Wadsworth, 1989).

There are several outstanding characteristics of the preoperational period, egocentrism, centration, reversibility and transformation. An egocentric child cannot stand in another persons shoes and see the world as they do, they are unable to take the view point of others and belive that everybody else thinks in the same ways they do. They are not even aware that other people have differennt view points. These beliefs are reflected in the way they interact with the world; in their language and their behaviours. In centration, a child only pays attention to a small range of aspects when observing a stimulis. They may only pay attention to the height of the object rather than its mass.

Reversability refers to the fact that reversible thoughts can follow their line of reasoning back to its starting point. Children of this age cannot think back to the initial stage of an action to answer a question pertaining to it. They cannot think in reverse. Finally, a similar characteristic to reversibility is transformation. Preoperational children are more focussed on states as opposed to the transformations between states. When children in this stage are asked to arrange sticks depicting a falling motion, most have trouble filling in the steps between the initial and the final states (Bjorklund, 1995).

All of these above characteristics are evident in the preoperational childs inability to solve conservation problems. Conservation is the realisation that mass stays the same even if an object changes form or appearance. Conservation cannot be taught, it must be learnt through the childs experiences and interactions (wadsworth, 1989). There are three main tests of conservation used in experiments, conservation of number, area and liquid.


The stage of concrete operations is observed in children of approximately the ages of seven to eleven. Children in this stage can think much more systematically and quantitatively. The child's reasoning processes become logical and they acquire operations; "systems of internal mental actions that underlie logical thinking" (Flavell, Miller & Miller, 1993). The children can now conserve and classify, they are no longer bound by egocentrism or perceptual centration and can follow the successive movements of a transformation.

The concrete operational child can conserve in all forms, number, area and liquid. Just as the little girl in the picture below can conserve liquid, so can the children in this stage. Not only can the children answer the conservation question correctly, they can give sound logical reasoning as to why the amounts of liquid are the same in the beakers, such as that it is higher in one glass because that one is thin whereas the other is wide.

Multiple classification is mastered by children in the concrete operational stage. This is when children have the ability to classify objects on more than one dimension such as colour and size. Class inclusion is also another classification system that is understood by children in this stage. In the earlier example in which oranges and apples were used to illustrate the principles of class inclusion, the concrete operational child would now be able to tell you that there are more pieces of fruit than there are apples. They can deal with sub-ordinate and super-ordinate concepts.

The egocentricity of the preoperational stage is almost non-existent, the child is now able to place herself in the positions of others and can solve the Three Mountain Problem in which the child can tell the experimenter the view the doll situated on one of the mountains has. The child is able to make a mental shift to the position of the doll.

The child has developed the ability to separate herself from particular aspects of a stimulus and can study the entire field of perception. This can be seen in an everyday example such as judging the age of a person (Bjorklund, 1995). When in the pre-operational stage, the child may judge age using a certain aspect such as height, the taller you are the older you are. Height however, is only one aspect of age and an unreliable one at that. Concrete operational children understand that many features come together when age is being judged and identified. This ability is the decentration of the child's perception of the world. She no longer focuses on one aspect.

Understanding transformations is a development, which takes place in the concrete operations stage. The child can now produce replications of the transitions between initial and final states of things such as a stick falling over. They can also order objects in hierarchical structures called seriation. She can rank objects in terms of dimensions such as height. This helps them to deal with numbers and mathematical problems (Le Francois, 2000).


(11 onwards)

The stage of formal operations is quite different from concrete operations. While both are logical and systematic thought functions, people in the formal operations stage can apply these processes to more abstract problems and hypotheses. This is Piaget’s last stage of cognitive development, after this he proposed “no further structural imrpovements in the quality of reasoning” (Wadsworth, 1989. pg.115). Unfortunately, it is believed that not all adults arrive at formal operations although most have reached their full potential by about 14 - 15 years of age.

There are several structures that are developed in this stage, hypothetico-deductive reasoning, scientific-inductive reasoning and reflective abstraction. Piaget (1981) described the capacity for hypothetico-deductive reasoning as the ability to be able to deal with not only objects and experiences but with hypotheses as well, with "the possible as well as the real". Conclusions can now be deduced from hypotheses rather than just physical facts. This highlights the persons ability to make conclusions by going from general to specific (deductive reasoning).

Scientific-inductive reasoning is the ability to think like a scientist, to make conclusions by going from specific observations to generalisations. When people in this stage have been confronted by a problem they can think about it abstractly, and can think over each of the different variables and how they, or combinations of them would affect the situation while sytematically testing for these. A common problem used to study this type of reasoning is the pendulum problem in which young people are given strings of different lengths that can be attached to a pole, they are also given objects of various weights to hang from the string and make pendulums. The underlying problem is to find out what it is that makes the pendulum swing faster, the length of string, the weight of the pendulum, the height from which the weight is dropped or the force exerted on the weight when it is dropped (Bjorklund, 1995). It is not till children reach the formal operational stage that they can systematically go about solving this problem and arrive at the correct and logical conclusion.

Another structure that has developed over this period is reflective abstraction, a mechanism by which knowledge (such as logical-mathematical) can be gained. According to Wadsworth (1989) “reflective abstraction is internal thought or reflection based on available knowledge”. Analogies provide a good example in which to study reflective abstraction. Analogies are about constructing relationships between objects, and these relationships can only come about through reflective abstraction.


Fun Educational Website

A general website that can be used to look up educational terms and theories.

Test of formal operations

This website is a fun test to do to see if and to what extent you have reached Piaget's level of formal operations.

Deb's fun page

This website is just for the pure amusment of those how have the time.