Conservation in psychology is the understanding that certain properties of objects – such as the volume of liquid, number of items, or the mass of a substance (like clay or dough) – stay the same even when their appearance or arrangement changes.
A classic example of a conservation task is pouring the same amount of water from a short, wide glass into a tall, narrow one and asking the child if the amount of water is still the same.
Conservation is a key concept in Piaget’s theory of cognitive development, showing up around age 7.
It reflects emerging logical thinking during the concrete operational stage.
How did Piaget study conservation in children?
Psychologist Jean Piaget came up with simple experiments, called conservation tasks, to see how children think about the world as they grow.
He would do things like pour the same amount of water into a tall, skinny glass and a short, wide one, then ask the child if both glasses still have the same amount of water (conservation of liquid).
Or he’d spread out one row of coins and bunch up another, then ask which row has more (conservation of number).
He also tested if kids could tell that a ball of clay is still the same amount even after it’s rolled into a sausage shape (conservation of mass).
He would also place two sticks side by side so they’re the same length, then move one slightly to the right, and ask if the sticks are still the same length (conservation of length).
In another task, he would show two identical shapes made from building blocks, then spread one shape out or rearrange the blocks, and ask if both take up the same amount of space (conservation of volume or area).
These tasks helped him understand how kids think at different ages.
Especially the shift from the preoperational stage (ages 2–7), when kids are easily fooled by appearances, to the concrete operational stage (ages 7–11), when they start thinking more logically.
At what stage of development do children understand conservation?
Children typically understand conservation during the concrete operational stage of Jean Piaget’s stages of cognitive development, which occurs between ages 7 and 11.
This means they realize that things like the amount of water, number of objects, or size of a lump of clay stay the same – even if they look different (like when water is poured into a taller glass).
Before this stage, in the preoperational stage (ages 2–7), children often focus on just one part of a situation (this is called centration) and have trouble mentally reversing changes (irreversibility).
But once they reach the concrete operational stage, they can think more logically and understand that appearances can be misleading.
Children’s ability to succeed on conservation tasks depends not only on age or stage of development but also on key aspects of executive functioning – specifically, working memory, cognitive flexibility, and inhibitory control.
Why do children fail conservation tasks before a certain age?
Children usually fail conservation tasks before age 7 because they’re in what Jean Piaget called the preoperational stage of cognitive development (ages 2–7).
At this stage, their thinking is limited by things like:
- Centration: They focus on just one part of a situation (like the height of a glass) and ignore other important parts (like the width).
- Irreversibility: They have trouble mentally reversing a change, like imagining the water going back into the original glass.
- Egocentrism: They often see the world only from their own point of view, and find it hard to imagine someone else’s perspective.
- Theory of Mind: This is the understanding that other people have thoughts, beliefs, and perspectives that may be different from one’s own. In early childhood, theory of mind is still developing, so children may not fully grasp that others could interpret situations differently.
These thinking patterns make it hard for them to understand that things like volume, mass, or number stay the same, even if they look different.
Once they reach the concrete operational stage (around age 7–11), they start thinking more logically and usually pass conservation tasks.
How does executive function support conservation understanding?
Children’s ability to succeed on conservation tasks depends not only on age or stage of development but also on key aspects of executive functioning.
Executive functioning is a set of mental skills that help you stay focused, plan ahead, remember instructions, switch between tasks, and control your behavior.
It’s like the brain’s control center, helping you manage your thoughts and actions to reach goals and make smart decisions.
There are three main parts of executive functioning:
- Working Memory:’This helps you hold information in your mind while using it.
- Cognitive Flexibility: This is your ability to switch between different ideas or ways of thinking.
- Inhibitory Control (Self-Control): This helps you stop yourself from doing something impulsive and think before you act.
For example, to understand that water poured into a taller glass hasn’t increased in volume, a child must:
- hold the original quantity in mind (working memory),
- consider both height and width at the same time (cognitive flexibility),
- and resist the impulse to say “more” just because the glass looks taller (inhibitory control).
These skills help children coordinate multiple dimensions of a problem and focus on relevant information, rather than being misled by changes in appearance.
As these executive functions mature – often around the same time as the transition to Piaget’s concrete operational stage – children become better at applying logical rules across different types of conservation tasks.
How does working memory help children to conserve?
To understand number conservation, kids need more than just logic – they need working memory, which is a part of the brain that helps you hold and use information in your mind for a short time.
Working memory is like the brain’s mental notepad.
It lets you hold on to information temporarily while you’re using it to solve a problem, make a decision, or understand something that’s changing.
In conservation tasks, working memory helps children remember what the setup looked like at the beginning, keep track of what changed, and mentally compare the before-and-after situations to figure out if the number stayed the same.
Without this ability, it’s easy to forget the original layout or get distracted by the way things look now.
Why is self-control (inhibitory control) important in conservation tasks?
Inhibitory control is the brain’s ability to stop an automatic or instinctive reaction and replace it with a more thoughtful, logical response.
It’s like a mental “brake” that helps us slow down and think before answering.
In Piaget’s conservation tasks, inhibitory control is important because young children often rely on how things look rather than what they actually know.
These tasks test whether a child can understand that certain things – like number, volume, or mass—stay the same even when their appearance changes.
For example, young children often make the mistake of thinking the longer row has more coins.
This is called the “length-equals-number” shortcut. It’s a natural reaction based on what they see.
To get the right answer, kids have to ignore what looks right and think logically.
That takes self-control. The brain has to block the quick, wrong answer and focus on what really happened. This ability grows with age and brain development.
To answer correctly, children need to resist this instinctive, but wrong, response.
This skill is part of the brain’s executive functions, which are still developing in early childhood.
Brain imaging studies (like those by Houdé and Poirel) show that successful children activate areas like the right inferior frontal gyrus – a region linked to inhibiting incorrect responses.
- Houdé et al. (2011): Showed that older kids (who answered correctly) used more brain areas linked to number thinking and self-control than younger kids.
- Poirel et al. (2012): Found that different brain areas have different jobs – one area helps with holding numbers in memory, and another helps with blocking the wrong answer.
Why is conservation important in understanding cognitive development?
Conservation is important because it shows how a child’s thinking becomes more logical and advanced as they grow.
It’s a key part of Jean Piaget’s theory of cognitive development, which explains how children’s thinking changes over time.
When a child understands conservation, it means they’re moving from the preoperational stage (ages 2–7) to the concrete operational stage (ages 7–11).
This shift tells us that they’re starting to overcome earlier thinking limits like centration (focusing on one feature) and irreversibility (not being able to mentally reverse a change).
By using conservation tasks, psychologists, teacher, and parents can measure how well a child is developing important skills like logical reasoning, perspective-taking, and even aspects of theory of mind.
These skills are essential for solving real-world problems, learning math and science, and understanding that appearances can be misleading.
So, conservation isn’t just about water in glasses – it’s a window into how a child’s brain is growing and becoming more capable.
Cognitive Development Timeline (Ages 3–11)
Ages 3–4: Early Thinking and Egocentrism
- Children begin to understand that others have different emotions and desires, but their thinking is still egocentric – they assume everyone sees the world as they do.
- They cannot yet pass conservation tasks; if a glass looks taller, they believe it holds more.
- Their brains are just beginning to develop skills like paying attention and remembering things (executive functions).
Ages 4–5: Beginning Perspective-Taking
- Many children can now pass false belief tasks (like the Sally-Anne test), showing the beginnings of theory of mind—they realize others can hold beliefs different from their own.
- However, they usually still fail conservation tasks due to centration (focusing on just one aspect, like height).
- They’re getting better at switching their attention and thinking in more flexible ways, but still need support.
Ages 6–7: Cognitive Shift and Conservation Emerging
- Children begin to show better inhibitory control and working memory, helping them handle more complex tasks.
- They start to succeed on simpler conservation tasks (like number or mass) as they move from the preoperational stage to the concrete operational stage.
- They can now think about more than one part of a situation at once, which helps with both conservation and understanding other people’s perspectives (decentering).
Ages 7–8: Logical Thinking and Conservation Solidifying
- Most children at this age can reliably pass conservation tasks involving volume, mass, and number.
- They think more clearly and logically and understand that appearances can be misleading.
- Their working memory and cognitive flexibility continue to improve, allowing for better reasoning.
- They also gain a stronger understanding of the difference between appearance and reality, a skill relevant to both conservation and theory of mind.
Ages 9–11: Maturing Cognitive Skills
- Children now use logical reasoning across many areas, such as solving math problems or understanding social situations.
- Their brain functions, like planning, solving problems, and switching between ideas, are much stronger (executive functioning).
- Their theory of mind is fully developed; they can understand complex beliefs, hidden intentions, and multiple points of view.
Conservation Tasks
Liquid Conservation Task
The teacher places two identical glasses of water side by side in front of the class. She asks the students if both glasses have the same amount of water.
Everyone agrees – yes, they’re the same.
Then, she pours the water from one glass into a taller, thinner glass. She asks again: “Which glass has more water, or are they the same?”
Response from a Preoperational Student (age 5):
“The tall glass has more water!”
A preoperational child (around age 4) may say that a taller, thinner glass has “more water” than a shorter, wider one, even though they saw the same water poured into both.
Their thinking is centered on appearance and they cannot mentally reverse the action.
The child is focused on height only and can’t mentally reverse the action of pouring. Their logic is based on appearance: taller means more.
Response from a Concrete Operational Student (age 8):
“They’re the same. You just poured it from one glass to the other.”
A concrete operational child (around age 8), however, understands that although the glass looks different, the quantity remains the same.
The child now understands reversibility – they can mentally reverse the action and realize no water was added or taken away.
They think logically, not just based on looks.
This illustrates a qualitative shift in reasoning: from intuitive to logical, irreversible to reversible, and egocentric to decentered thinking.
Number Conservation Task
This task shows how conservation of number reflects logical operations and reversibility – key abilities that emerge in the concrete operational stage.
🧑🏫 Activity Setup:
A teacher places two rows of coins on the table:
- Row A: 5 coins spaced evenly
- Row B: 5 coins spaced evenly
- Both rows are aligned one-to-one, so each coin in Row A directly matches a coin in Row B.
Step 1 – Initial Question:
🗣️ Teacher asks: “Do these two rows have the same number of coins?”
✅ Most children, regardless of age, say: “Yes.”
This shows basic one-to-one correspondence, even in preoperational children.
Step 2 – Transformation:
The teacher spreads out the coins in Row B, making the row visibly longer.
🗣️ Teacher says nothing—just spreads them silently.
Importantly, the quantity remains unchanged; only the spacing has altered.
Step 3 – Final Question:
🗣️ Teacher asks again: “Now, do both rows still have the same number of coins, or does one have more?”
🧒 Response from a Preoperational Child (age ~4–5):
“No, the longer row has more.”
The child is focusing on appearance (length), not logic.
- The child is engaging in centration—focusing on a single, striking feature (length).
- They lack reversibility, so they can’t mentally “undo” the spacing transformation.
- Their answer is driven by perceptual appearance rather than logical reasoning.
This aligns with preoperational thinking, where logic is intuitive and appearance-based.
👧 Response from a Concrete Operational Child (age ~7–8):
“Yes, they still have the same number. You just spread them out.”
The child understands number conservation and can mentally reverse the change.
- This child uses logical operations to reason that the transformation didn’t add or remove coins.
- They demonstrate reversibility—they can mentally return the coins to their original configuration.
- This is a sign of conservation of number, a major milestone in the concrete operational stage.
Classroom Tips
- Ask follow-up questions, like: “How do you know they’re still the same?” to reveal the child’s reasoning.
- Have children explain their thinking to each other—peer discussion can support conceptual growth.
Conservation of Volume vs. Liquid
Some textbooks use the terms volume and liquid conservation interchangeably.
However, in Piagetian theory, they refer to two different types of conservation tasks, each assessing slightly different aspects of a child’s thinking.
Why They’re Often Confused:
- Both involve understanding that quantity stays the same despite changes in appearance.
- Both seem to involve “volume” in everyday language – e.g., “How much space does something take up?”
The Key Difference:
- Conservation of Liquid involves continuous substances (like water, juice, or milk). The focus is on whether children understand that the amount of liquid remains constant when it’s poured into containers of different shapes, such as a short, wide glass versus a tall, narrow one.
- ✅ What it tests: Logical reasoning about fluid displacement and container shape.
- Conservation of Volume (or area/space) typically involves solid objects, such as blocks or shapes made from clay. The child must judge whether the space something occupies is still the same after it’s been rearranged, stretched, or flattened.
- ✅ What it tests: Spatial reasoning—understanding that rearranging parts doesn’t change the total space taken up.
Why It Matters for Teaching:
- Liquid conservation tasks often come earlier in development and are more intuitive to set up.
- Volume/area tasks involve more advanced spatial skills and can be more abstract, especially for younger children.
- Understanding the difference helps teachers choose the right task for the right developmental level and avoid misinterpreting student errors.
Criticisms and Alternative Views
1. Underestimation of Children’s Abilities
One of the most common criticisms of Piaget’s theory is that it may underestimate the cognitive abilities of young children.
Later studies, such as those by Donaldson (1974), found that with simplified procedures and more contextually meaningful tasks, children as young as 4 or 5 could demonstrate understanding of conservation.
This suggests that children’s performance on Piagetian tasks may not fully reflect their underlying competence, but rather the complexity or unfamiliarity of the tasks themselves.
McGarrigle and Donaldson (1974)
A feature of the conservation task which may interfere with children’s understanding is that the adult purposely alters the appearance of something, so the child thinks this alteration is important.
McGarrigle and Donaldson (1974) devised a study of the conservation of numbers in which the alteration was accidental.
When two identical rows of sweets were laid out and the child was satisfied there were the same number in each, a “naughty teddy” appeared. Whilst playing around, teddy actually messed up one row of sweets. Once he was safely back in a box the children were asked if there were the same number of sweets.
The children were between four- and six-years-old, and more than half gave the correct answer.
This suggests that, once again, Piaget’s design prevented the children from showing that they could conserve at a younger age than he claimed.
2. Underestimates Cultural Factors
Piaget’s theory suggests that all children develop cognitive abilities like conservation in a fixed sequence based on age, regardless of their background or environment.
However, cross-cultural research shows that this isn’t always the case -how and when children develop these skills can vary depending on their culture and experiences.
For example, a study with Wolof adolescents in Senegal found that many failed Piaget’s standard liquid conservation task (Dasen, 1994).
But this wasn’t due to a lack of understanding. In Wolof culture, children aren’t used to being asked questions where the answer is already known – something common in Western-style testing.
When the task was reframed as a language-learning activity, the children showed they did understand conservation after all.
Other studies show that children might seem less capable than they actually are if the test uses unfamiliar materials, is presented in a confusing way, or if the children haven’t been to school.
These factors can affect how they understand the task – not their true ability (Dasen, 1972; Serpell, 1979).
subsistence-based culture
A subsistence-based culture is a society where people primarily produce just enough food, goods, or resources to meet their basic daily needs, rather than for trade, profit, or accumulation of wealth.
In subsistence-based cultures, children often help with daily tasks like cooking, farming, or collecting water.
These real-life activities involve skills such as measuring, estimating, and problem-solving.
As a result, children may develop certain cognitive abilities (like conservation) earlier than expected (Greenfield, 1966).
This can happen even without formal schooling.
Overall, this research shows that cognitive development isn’t just about age or biology – it’s also shaped by the culture, tools, and experiences children grow up with.
3. Task Demands and Language Confusion
Conservation tasks may not fully reveal a child’s true understanding because they rely on passive observation rather than active involvement.
The 2016 study suggests that when children physically engage with the materials (rather than just watch an adult), they perform better.
This implies that Piaget’s original method may have underestimated children’s abilities by not allowing them to learn or demonstrate understanding through action, which is a form of task demand.
Lozada and Carro (2016) found that 6–7 year-old children understood conservation better when they could do the task themselves, rather than just watch an adult do it.
For example, when kids poured water, moved coins, or shaped clay with their own hands, they were much more likely to say that the amount stayed the same – even if it looked different afterward.
This supports a theory called embodied cognition, which says that we learn better when we’re physically involved.
According to this idea, thinking and doing are connected – our brains understand things more deeply when we use our bodies, like touching, moving, or seeing changes up close.
It’s not just about watching and remembering—it’s about doing and experiencing.
This hands-on approach helps them see that, even if something looks different (like water in a taller glass), the amount stays the same.
Piaget’s conservation tasks can be confusing – not because of the thinking required, but because of how the questions are asked.
If a child is asked the same question twice (before and after the change), they might assume their first answer was wrong and change it.
This is known as a demand characteristic in experimental psychology.
Rose and Blank (1974) argued that when a child gives the wrong answer to a question, we repeat the question in order to hint that their first answer was wrong.
This is what Piaget did by asking children the same question twice in the conservation experiments, before and after the transformation.
When Rose and Blank replicated this but asked the question only once, after the liquid had been poured, they found many more six-year-olds gave the correct answer.
This shows children can conserve at a younger age than Piaget claimed.
Samuel and Bryant (1984)
Samuel and Bryant (1984) investigated whether Piaget’s tests of conservation were flawed because the children were responding to being asked the same question twice.
Research questions:
- How does asking only one question about conservation affect the ability of children over a wide age range?
- Are conservation of mass, number, and volume all affected?
Procedure:
- 252 boys and girls aged 5½ -8 years old were divided into four groups (by age).
- This study used an independent measures experimental design.
- Each group was subdivided into three conditions: standard (pre and post-transformation questions); one judgment (post-transformation question); fixed array (child didn’t see transformation).
- Squashed cylinders were used to test mass, spread out rows of counters for number and tall/narrow glasses for volume.
Findings:
- Children performed better with only the post-transformation question (for most ages and most
materials, oddities being due to chance) - Older children were better at all tasks than younger
ones. - The standard Piagetian was harder than both the post-transformation question only and the fixed array situation.
- The number task was the easiest.
Conclusion:
- Samuel & Bryant conclude that the problem lies with the effect of the experimenter asking a second question and unwittingly implying to the participant that a different answer is required.
- Asking both the pre and post-transformation questions causes children who can conserve to make conservation errors.
Evaluation:
- Samuel and Bryant tested 252 children which is a large sample. They tested children from the age of five to the age of eight which allowed them to draw conclusions about the age at which children started to be able to conserve.
- They all came from one area of the country (Devon) which might mean that they are not representative of children from other areas of the country. For example, if Devon used different teaching strategies to other parts of the country this might have an effect on the children’s cognitive
abilities. - This is not really a criticism of the study and overall the sample is large enough to allow generalisations to be made.
- The task itself is quite an artificial one. It is not an everyday occurrence to ask children this type of question, although the skills that are being tested are everyday skills.
- Perhaps a more ecologically valid method would have been to ask children to choose which of two beakers of juice or rows of smarties they would prefer to have. This would be more ‘real’ to the children as well as demonstrating clearly that they could conserve.
- There are some difficulties in evaluating the actual question used as the researchers do not tell us the exact wording of the question. Asking a child ‘are they the same?’ may be a slightly ambiguous question.
- There are many ways in which this question might have been asked and it is possible that children may
have interpreted the question differently.
Porpodas (1987)
Porpodas (1987) found that asking more than one question wasn’t really the problem.
This research suggested that the questions provided ‘verbal interference’ which prevented children from transferring information across from the pretransformation stage.
This implied that the problem was a cognitive one, but not exactly of the nature originally suggested.
Baucal & Stepanovic (2006)
In an attempt to answer the ‘conservation or conversation?’ question, ie whether the conservation failures are due to cognitive immaturity or the language use or power relations between the child participant and adult experimenter, Baucal & Stepanovic (2006) analyzed the results of many tests of the repeated question hypothesis.
They also conducted an additional test which aimed to distinguish between cognitive and social effects by using a repeated question about a ‘transformation’ which had not changed (pouring liquid back into the same glass so only the question and not the actual change could influence their
response).
Interestingly, the results were not as predicted. They expected that any child’s response would be the same on the standard and modified tasks, but this was not the case.
However, they were unable to conclude whether the cause was or was not repeating the question.
Arcidiacono and Perret-Clermont (2009)
Research has gone on to explore the ‘conversation about conservation’ idea which underpins the interview method.
Arcidiacono and Perret-Clermont (2009) suggested that children’s statements about conservation are not, as Piaget claimed, simply a product of their cognitive level but of their social interaction with the interviewer.
This suggests that the child’s reasoning is ‘co-constructed’ during the testing process. If adult ‘accept’ wrong (or right) answers without asking for a justification (argument about why it is so), which is what Piaget was really interested in.
4. Alternative Theories
While Jean Piaget was the first to identify conservation as a key sign of logical thinking, other major cognitive theories also help explain how and why children come to understand that quantity stays the same even when appearance changes
Each theory agrees that conservation is an important part of cognitive development, but they explain it differently:
- Piaget: A stage-based shift in thinking, especially during the concrete operational stage.
- Information processing theory: A gradual improvement in memory, attention, and reasoning.
- Sociocultural theory: A skill that develops through guided interaction and cultural learning.
- Constructivism: A concept children build through direct, active experience.
By comparing these views, we can better understand conservation as a multi-dimensional milestone that reflects both internal brain development and external learning experiences.
Information Processing Theory
Information processing theory compares the human mind to a computer, focusing on how children take in, store, and use information.
From this perspective, conservation becomes possible as children’s executive functions – like working memory, attention control, and processing speed – improve.
For example, in a liquid conservation task, the child needs to remember the original amount, compare it with the new appearance, and resist the misleading visual cue.
According to this theory, success on conservation tasks isn’t just about “stages”—it’s about the brain getting better at managing complex information over time.
Vygotsky’s Sociocultural Theory
Lev Vygotsky emphasized the role of social interaction and cultural tools (like language and symbols) in learning.
He believed children could learn to conserve earlier than Piaget suggested, especially with the help of an adult or more skilled peer.
This support is called scaffolding, and it takes place in the zone of proximal development (ZPD)—the range between what a child can do alone and what they can do with help.
Vygotsky would argue that conservation is not just discovered through independent exploration, but often taught and co-constructed through guided experiences.
Constructivist Learning Theory
Both Piaget and Vygotsky are considered constructivists, but Piaget focused more on independent exploration, while Vygotsky focused on social learning.
Constructivist theory, in general, says that children build knowledge through active engagement with the world.
In the case of conservation, this means children develop the concept over time by interacting with objects, testing ideas, and reflecting on outcomes.
Hands-on experiences (like pouring water between containers or reshaping clay) help children discover conservation principles on their own.
5. Linking Conservation to Theory of Mind
Theory of Mind (ToM) is the ability to understand that other people have their own thoughts, beliefs, feelings, and intentions that may be different from your own.
Understanding conservation and succeeding on theory of mind (ToM) tasks both require children to move beyond surface appearances and reason about what is actually true versus what someone might believe to be true.
For example, in a classic false belief task, a child watches as a toy is moved from a basket to a box while another person is out of the room.
To pass the task, the child must recognize that the other person will falsely believe the toy is still in the basket. This requires the child to hold two perspectives in mind at once—their own (true location) and the other person’s (false belief).
Similarly, in a conservation task, a child must understand that even though water looks like “more” in a taller glass, the actual quantity hasn’t changed.
Both tasks require the ability to decenter—that is, to mentally juggle multiple viewpoints or dimensions at the same time.
This connection suggests that as children’s cognitive flexibility and representational understanding improve, they gain new insight into both physical and mental states that may not match how things appear.
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