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Judith Samuel and Peter Bryant (1984)

Asking only one question in the conservation experiment



Samuel and Bryant's experiment is one of many studies which have attempted to challenge Piaget's theory of cognitive development through criticising his methods.  It is important that we firstly understand Piaget's theory of cognitive development.

Bandura's social learning approach to child development maintains that development is simply a process of learning more as one gets older.  So, for example, cognitive or moral progress for Bandura was merely a process of learning more - quantitative change.

However Piagetís structuralist approach to child development provides a very different account of child development.  For example, Piaget believes that development is a systematic, structured process.  Piaget believes that it is not just the amount of knowledge which distinguishes a young child from an older child.  There is actually a qualitative difference in their thoughts.  To Piaget, changes in the way a child thought about the world signified a change in cognitive, or intellectual development.  As the child's intellect develops, it becomes increasingly capable of carrying out actions upon its environment which will ensure its survival.

The Swiss psychologist, Jean Piaget, put forward one of the most influential structuralist theories about how a childís mind develops.  Piaget thought that intellectual development happened in stages, and that a child would only go on to the next stage once it had completely mastered the first one.  Each stage is seen as a kind of 'building block' for the next stage to rest on.  In each stage, Piaget said, the child would develop new ways of thinking which had developed out of what went before, but which were different from previous ways.

Piaget outlined four stages of cognitive development, and gave approximate ages at which children reached those stages.  He stressed, though, that these ages are only averages; individual children might go through the stages at a different speed but they would always go through the stages in the same order.  These maturational stages, in brief, are:

1. Sensory motor stage (birth to around 18 months).   During this stage the child gains understanding of its environment by using its senses in combination with movement.  

2. Pre-operational stage (18 months to about 7 years).  During this stage the child becomes able to represent objects or events by symbols or signs.     The child is now able to use language and express ideas.  The child is also developing some general rules about mental operations.

3. Concrete operational stage (7 to around 12 years).  During this stage the child is able to use more sophisticated mental operations.  For example, the child is said to have decentred.  Decentring simply means being able to take account of more than one aspect of a situation.   However the child is still limited in a number of ways, for example, they tend to think about the world in terms of how it is, and find it hard to speculate on how it might be.

4.  Formal operational stage (12 years and above). This stage is mainly governed by formal logic and is the most sophisticated stage of thinking.

Piaget devised numerous tests which highlighted the errors children make with certain problems.  These errors demonstrated the different quality of thought children have in different stages.  

One of the most well known tests Piaget used to show the limitations of child thinking in the pre-operational stage was the conservation experiment.

In one of his conservation tests Piaget demonstrated that if you show a child two beakers of water, one of which is tall and thin, the other short and fat, and ask the child which beaker contains the most water, the pre-operational child (i.e. child under 7) will say 'the tall one', even though they both contain the same amount of water.  Piaget argued that this is because the child has not developed the ability to conserve volume, which does not develop until the child is in the concrete operational stage.  Conservation of volume is the ability to realise that something may have the same volume, even though it is a different shape.

Similarly he demonstrated that if you roll a piece of clay into a sausage shape, show it to a pre-operational child and then roll it into a ball, the child will say that there is more clay in the sausage shape.

Piaget also demonstrated that, if you present a pre-operational child with a row of five buttons spread out and a row of five buttons close together, the child will say that the spread-out row contains more buttons.

Piaget argued that the inability to conserve is due to the child's failure to understand that things remain the same (constant) despite changes in their appearance (how they look).  Piaget believes this is an example of centration.  The pre-operational child has not decentred and is therefore centring on just one dimension.  For example, the child is centring on just one dimension of the beaker, usually its height, and so fails to take width into account.

Piagetís work has given psychologists many insights into the qualities and limitations of child thought.  However, from the late 1970s onwards, there have been many replications of Piaget's methods, which have demonstrated that Piaget often underestimated the cognitive abilities of children.  In particular, it is argued that Piagetís findings were a result of the structure of his original tests rather than the limitation of child thought.



The aim of Samuel and Bryantís study was to challenge Piaget's findings by altering the method used by Piaget.



The participants were 252 boys and girls between the ages of 5 and 8.5.  They were all in schools and playgroups in and around Crediton, Devon.  They were divided into four age groups of 63 children, whose mean ages were;

5 years 3 months

6 years 3 months

7 years 3 months

8 years 3 months

Each group was divided into 3 subgroups which underwent a different condition.

The three conditions were:

1    Standard:  This is the traditional two question conservation task as carried out by Piaget.  The child is asked about the size of the object before and after the shape was changed.

2    One judgement: This is a conservation task like the original but this time with only one question asked, the post transformation question.  That is, the child is only asked once about the size of the object and this is after the transformation has taken place.

3    Fixed array control: In this condition the child saw no transformation being made and only saw the post-transformation display.  That is, the child just saw the objects after they had been changed and not before.  The purpose of this third condition was to check that children who answered the post-transformation question correctly in the other two conditions did so by bringing over information from the pre-transformation display.

Three different types of material were used for the conservation tasks.

(a) Mass:  In this task children in condition 1 and 2 were first shown two equal and identical Playdoh cylinder shapes.  The transformation was to squash one of these shapes into a sausage.  After this, the children were asked to compare the cylinder and the sausage.  The children in condition 3 also made this comparison without seeing the first display or the transformation.

(b) Number:  In this task children in condition 1 and 2 were shown two rows of counters of equal length arranged side by side in one to one correspondence.  The rows contained six counters.  Then one row was spread out or bunched up.  The condition 3 children saw only the post-transformation displays.

(c) Volume:  In this task children in conditions 1 and 2 were first shown two identical glasses with the same amounts of liquid.  Then the liquid from one glass was poured into a narrower one or a shallow wider one.  The condition 3 children saw only the post-transformation displays.

Each child was given four trials with each kind of material and the order of the tests was systematically varied between the children.

Therefore there are three independent variables. 

The three conditions, the four age groups and the three kinds of materials used.

The dependent variable was the number of errors made by the children.





The researchers recorded the number of errors children made in the tests.  Examples of errors would include when a child said one lump was bigger than the other, or one row had more counters than the other, or one glass had more liquid than the other. The researchers made the following conclusions.


1.  As predicted by Samuel And Bryant, children found the one judgement task significantly easier (they made less errors) than the standard conservation task and the fixed-array control.  This was true of all three types of material.

 Samuel and Bryant also found that;

2.  There was a significant difference between the age groups, with older groups doing consistently better than the younger.  

3.  The children made fewer errors on the number task compared with the other two tasks



Samuel and Bryant give an explanation for why children make fewer errors on the one judgement conservation task compared to the standard conservation task. They believe that in the standard conservation task, the pre-transformation question is unwittingly forcing the child to give the wrong answer by asking the same question twice (they call this the extraneous reason hypothesis).

For example if the child is asked a question about the volume of beakers and then sees the experimenter pour the liquid from one beaker into another, the child might believe that the experimenter must be doing it for a reason and therefore want the child to give a different answer.

The ability to conserve (or understand the principle of variance as Samuel and Bryant put it) marks the end of pre-operational thought and the beginning of operational thought (at about seven) and is a significant landmark within Piaget's theory of cognitive development.

However Samuel and Bryant's experiment and many other studies have challenged Piaget's explanations of conservation by criticising his methods.  Samuel and Bryant demonstrate that the tasks used by Piaget actually made it difficult for children to give the correct answers and demonstrate that children below the age of seven can conserve.

Piagetís theory of cognitive development explained how a childís ability to think progresses through a series of distinct stages as they mature.   Piaget believed that these stages were maturational.  That is, development is genetic and largely unaffected by environmental factors.

However, Samuel and Bryant advocate a cognitive approach to child development.   According to this perspective, as children learn more about their world they will adopt new strategies with which to process information.  Therefore children who do not demonstrate the ability to conserve have simply not acquired the strategies for this skill or are not applying the skill correctly.

Despite this the Samuel and Bryant experiment did demonstrate two findings which support Piaget.

Firstly, they found that older children did do significantly better than younger children on the conservation tasks.  8 year olds did significantly better than 7 year olds, who did significantly better than 6 year olds, and so on - perhaps supporting Piaget's stage approach.

Secondly, they discovered, like Piaget, that children could conserve number before they could conserve mass and volume tasks.


Evaluation of Procedure


The main strength of Samuel and Bryantís experiment was the amount of control they had over possible confounding variables.  The children had to do four attempts at each conservation task which eliminates the possibility that the children answered incorrectly or correctly by chance, and order effects were controlled for by varying the order of the tasks. 

A weakness of the number task was that the children could have counted the number of counters used and this could account for the level of accuracy on the number task. 

A further weakness could have been that the children may have felt nervous doing the tasks (perhaps the younger children more so) and therefore resulted in the answers being spontaneous rather than thought out.


Evaluation of Explanation


Samuel and Bryant argue that Piaget's theory of cognitive development places too much emphasis on maturational factors.  Using a cognitive approach they believe that children learn new strategies and skills.  Samuel and Bryant also criticise Piaget for emphasising how children learn as individuals.  Samuel and Bryant argue that children do not learn in isolation, and that they learn far more readily and efficiently when they are working together than when they are alone.

However two of Samuel and Bryant's findings do support Piaget's theory and Piaget's theory is still one the most influential theories of child thought.  Of particular value are Piagetís insights into how children do think about the world qualitatively different to adults.   



Samuel, J. & Bryant, P. (1984) Asking only one question in the conservation experiment. Journal of Child Psychology and Psychiatry, 25, 315-18.





GROSS, R. (1999) Key Studies in Psychology, 3rd Edition. London: Hodder and Stoughton

BANYARD, P. AND GRAYSON, A. (2000) Introducing Psychological Research; Seventy Studies that Shape Psychology, 2nd Edition. London: Macmillan