IB Psychology SLTopic 2 — Human DevelopmentPaper 1 & 2Cognitive approach~13 min read
Piaget’s Stages of Cognitive Development
Piaget’s claim was not that young children know less than adults. It was that they think in a completely different way — and that the way changes in a fixed order. The famous tasks in this page are designed to make that difference visible in about thirty seconds.
📘 What you need to know
Children’s thinking is qualitatively different from adult thinking, not just a smaller version of it.
Development is maturational: the stages follow a biological timetable and always come in the same order.
Children learn by exploring, like little scientists — this is discovery learning.
A schema is a mental file for how something works. Schemas grow through assimilation and accommodation.
Four stages: sensorimotor, pre-operational, concrete operational, formal operational.
Key markers: object permanence, egocentrism, conservation, class inclusion, abstract reasoning.
Classic tasks: the conservation task, the three mountains task and the class inclusion task.
Schemas: the child’s filing system
A schema is a mental file for a kind of thing. A toddler has a “dog” file: four legs, fur, barks. Every new animal gets checked against the files.
Assimilation
The new thing gets pushed into a file that already exists.
Example: the toddler sees a sheep and says “dog”. Four legs, fur — close enough. The file did not have to change.
Accommodation
The file itself has to be rewritten because the new thing does not fit.
Example: someone says “that’s a sheep, it says baa”. Now a new file is made and the dog file gets a stricter rule.
Assimilation keeps your existing ideas and squeezes the world into them. Accommodation changes your ideas to match the world. Almost every learning moment is a mix of the two, and the uncomfortable feeling when something does not fit is what pushes development forward.
Piaget’s framework
Genetic epistemology — knowledge is built by the child’s own drive to explore, unfolding through age-related stages rather than being poured in by adults.
The four stages
The key marker under each step is the ability a child gains by the end of that stage. Examiners often ask for exactly these.
Stage
Age
What thinking is like
Key marker
Sensorimotor
0–2 years
The child knows the world through senses and movement. Thinking happens through doing.
Object permanence at around 8 months — things still exist when hidden.
Pre-operational
2–7 years
Language explodes. Pretend play, treating objects as if alive, early ideas of time.
Egocentrism fades; the child starts to see other viewpoints.
Concrete operational
7–11 years
Logical thinking works, but only about real, concrete things in front of them.
Conservation of number, mass and volume is understood.
Formal operational
11 years and up
Abstract and hypothetical reasoning. Systematic problem solving and arguing about ideas.
Abstract reasoning — thinking about things that are not there.
Object permanence and the A-not-B task. A toy is hidden under cloth A several times, then, while the baby watches, hidden under cloth B. A baby who still reaches for A has not fully worked out that objects keep existing independently of the baby’s own actions.
The conservation task
This is the most famous demonstration in developmental psychology, and it takes two glasses of juice.
🧩 How the task is run
Show two equal amounts side by side — two identical glasses filled to the same line.
Ask first: does this one have more, does that one have more, or are they the same?
Change one while the child watches. Pour one glass into a taller, thinner one.
Ask exactly the same question again.
Judge the answer. “Still the same” = pass. “The tall one has more” = fail.
The liquid in the tall glass really does look like more. Passing means trusting logic over what your eyes are telling you — which is genuinely hard at five.
The three mountains task
This one tests egocentrism: the inability to picture a scene from anywhere except where you are sitting.
🧩 How the task is run
Show a model of three mountains with different features — a hut, a tree, some snow.
Place a doll on the far side, looking at the model from a different angle.
Ask: what does the doll see?
Offer photographs of the model taken from several positions and let the child choose.
Judge: around age 4 children usually pick their own view. By 7 or 8, most pick the doll’s.
Notice what all three tasks have in common. Each one asks the child to hold two things in mind at once — the appearance and the reality, their view and the doll’s, the part and the whole. That is really what Piaget’s stages are tracking.
The class inclusion task
This tests whether a child can see that a smaller group sits inside a bigger one.
Children who fail are not being silly. They hear “more daffodils or more flowers” as “more yellow ones or more red ones”, because holding a category inside a category is the skill still missing.
Evaluating Piaget’s theory
Strengths
Limitations
Testable. The tasks are simple, standardised and easy to repeat, so the findings are reliable.
Underplays language. Children may fail because of how the question is worded, not because the logic is missing.
Groundbreaking. It changed how psychology and schools view children, and sparked decades of research.
Weak original evidence. His early ideas came from a small, unrepresentative sample of Swiss children, including his own.
Practical impact. Age-appropriate curricula and hands-on primary teaching grew directly out of this work.
Underestimates children. Simplified versions of his tasks are passed by much younger children than he claimed.
Clear predictions. Because the stages are ordered, the theory can be proved wrong — a mark of good science.
Ignores the social side. Vygotsky’s criticism: children do not develop alone, and Piaget barely uses other people.
Link to concepts
Bias: the three mountains task assumes children know what mountains look like. It is built on Swiss landscapes. Conservation tasks assume Western ideas about measuring volume and number.
Responsibility: testing young children needs informed consent from a parent, protection from distress, and very careful wording, because children do not interpret questions the way adults do.
Measurement: a pass or fail on one task is a crude measure of something as complex as reasoning, and repeating a question can push a child into changing a correct answer.
Exam practice
EXAM QUESTION
Contrast two models of human development. [22]
“Contrast” means differences only. Do not waste half the essay listing what Piaget and Vygotsky agreed on.
Set up both models briefly
Piaget: maturational stages, child as little scientist. Vygotsky: social, ZPD and scaffolding.
Contrast 1 — what drives developmentPiaget: biology sets the pace → learning follows. Vygotsky: interaction leads → development follows.Contrast 2 — the role of other people
Piaget: children discover alone. Vygotsky: an MKO is essential.
Contrast 3 — stages
Piaget has four fixed stages; Vygotsky has none.
Contrast 4 — culture
Piaget assumes one universal sequence; Vygotsky expects development to differ by culture.
Support each contrast with a study, not just an assertionconservation task for Piaget, Conner & Cross for Vygotsky
💡 Exam tips
Learn the four stages with their key markers. A stage name alone rarely earns full credit.
Describe one task in real detail rather than naming three. Detail is what separates bands.
Remember qualitatively different — it is the phrase that captures Piaget’s central claim.
Assimilation and accommodation are easiest to explain with one concrete example each. Have your example ready.
The strongest criticism is that the tasks may test language, not logic. It applies to all three tasks.
If the question says “contrast”, write differences only. If it says “compare and contrast”, you need both.
⚠ Common mix-ups
Treating the ages as fixed. The order is fixed; the ages are averages and children vary.
Confusing assimilation and accommodation. Assimilation keeps the schema, accommodation changes it.
Saying egocentrism means selfish. It means unable to take another viewpoint — a thinking limit, not a character flaw.
Mixing conservation with class inclusion. Conservation is about amount staying the same; class inclusion is about groups inside groups.
Writing that Piaget ignored the environment. He built the theory on children exploring their environment — he underplayed other people.
Claiming object permanence appears at birth. Piaget placed it around 8 months, in the sensorimotor stage.
Up next: Theory of Mind: Understanding Other Minds — egocentrism was Piaget’s word for it, but the modern research asks the same question with much sharper tasks.
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