The Psychology of Intelligence: A Theory of Intelligence and Cognitive Development Between Birth and Adolescence

Researcher Jean Piaget’s theory of learning led to him being celebrated as the founding father of child psychology.

Home » Book Summaries » The Psychology of Intelligence: A Theory of Intelligence and Cognitive Development Between Birth and Adolescence

Karsen: From The Parent’s Club, I’m Karsen Kolnicki. This is your briefing.


Karsen: Today, we’re discussing The Psychology of Intelligence: A theory of intelligence and cognitive development between birth and adolescence by Jean Piaget

This title, known as one of the most important pieces on children's psychology, outlines how kids' minds work from birth to adolescence. The author's theory characterizes four stages of development and goals children should achieve at each stage.

Karsen: Vincent Phamvan on the key takeaways [pause] and what you need to know.


Karsen: Vincent, why are this book and Piaget's theory of intellectual or cognitive development vital in education and psychology?

Vincent: This work is classified as an essential part of understanding learning. Beforehand, researchers in child psychology wanted answers to the questions: What do children get wrong, and how can we test their intellectual abilities? Piaget first set out to answer these questions but came to find this wasn't the way to understand child intelligence. He noticed that children of similar ages tended to make the same mistakes and what they got wrong didn't give insight into their intelligence. It was how they made mistakes that they did.

This was such a monumental shift in thinking. It's no surprise that Psychology Today pronounced Piaget the Best Psychologist of the twentieth century.

Karsen: What got Piaget into researching this topic?

Vincent: Piaget was giving lectures on the psychology of intelligence in 1942 when psychology and studying the mind relatively new. Piaget's question to solve was: What is intelligence?

Karsen: That seems like a simple question with a complex answer. So what was his answer?

Vincent: Well, ultimately he found that intelligence is action. But, to get to this answer, he had to consider and reject earlier theories of intelligence. For example, there are philosophers that argue intelligence is the acquisition and correction of information we collect from the external world around us. This view is that we learn by making copies of things and their relationships.

But, in his research, Piaget found this to be wrong. Children who performed cognitive tests didn't appear to be accessing objective reality and copying information from it. They were actively constructing knowledge.

Karsen: How did he know this? What about his observations made him disagree with what previous philosophers argued?

Vincent: Toddlers, he observed, poke, prod, and pull at everything around them. Later on, children perform mental actions that have the same purpose: they rotate objects, put things in order, and compare different classes of things in their minds.

These actions, he came to believe, define intelligence. Even if we grant that “1 plus 1 equals 2” is an objective truth, a child can only arrive at this knowledge by actively reconstructing it for themself. Meaning, they must add 1 and 1 together rather than leaving them apart.

Karsen: So intelligence comes down to teaching concepts and applying those concepts to other situations.

Vincent: Yes, so if a child is able to combine 1 plus 1, they can separate them again and end up back where they started. Piaget concluded that intelligence consists of these exploratory actions.

Karsen: How is intelligence linked with exploring our environment?

Vincent: Piaget says adaptation governs all interactions between organisms and their environments. What this means is actions are driven by adapting to given situations. He argues that if you want to understand the relationship between things, look at how they adapt. For example, think of our digestive systems. When we eat something, our digestive system reacts to this sudden intrusion of foreign matter into the body by releasing acids and triggering abdominal muscles to contract. This is an example of accommodation or a type of adaptation in which an organism changes its structure in response to an interaction with its environment.

Karsen: Wouldn't that be more of a passive response since we do that multiple times a day, without noticing it?

Vincent: Yes, but there is also an active form of adaptation called assimilation. Digestion is both passive and active. When we eat an apple, our stomachs transform a part of the environment – the mass of fibre and vitamins we call apples – into a substance compatible with human life: energy. When an organism assimilates, it is actively imposing its own structure on the environment, just as our stomachs “restructure” the part of the environment made up of apples. Assimilation incorporates a part of the external world into ourselves.

Karsen: Oh, okay that makes sense. But what does this have to do with determining intelligence?

Vincent: Accommodation and assimilation don’t just determine our physical interactions with the environment, they also shape our mind or cognitive relationship with the world. Piaget found that we organize knowledge to adapt our minds to the world.

As we know, the world is full of information and every second we are bombarded with new information and things going on around us. This constant flow of incoming data would be overwhelming if we weren’t able to organize it somehow.

Karsen: Is there a certain way that we organize this information?

Vincent: We have schemas, which are like blueprints that act as filing cabinets to organize information about the world or how to behave in it. When we interact with our environment, we consult this cabinet to see if there’s anything in there that can help us make sense of what’s in front of us.

Karsen: Can you give an example of how a schema would help a child interact with the world?

Vincent: Yes, the book gives an example of a girl seeing a thorn for the first time. She doesn’t know what this object is, so she touches it and promptly pricks her finger. Because she didn’t have a “thorn schema,” she resorted to a different one like the “find out what things are by grabbing them” schema.

Karsen: Ouch, I definitely have used that schema though. So she grabs the thorn and realizes that schema wasn't the best. What happens the next time she sees a thorn? Will she do the same thing?

Vincent: Her new experience is stored away as a visual representation of a thorn linked to a specific memory, which is touching the thorn. This schema combines several ideas to create a behavioral script. It may say, sharp spikes growing on plant stems, cause pain and injury – so it’s a good idea not to grab them.

Karsen: Now she will hopefully remember this and be smart enough not to touch a thorn the next time she sees one.

Vincent: Exactly. This is how Intellectual assimilation and accommodation drive cognitive development. The book gives an example of a young boy on a walk with his mom. They stop at a tree and she points at a squirrel and asks her son what animal it is. He eagerly responds, "It's a dog!"

There are a couple of things we can say about this answer. First, it's wrong. But, at the same time it is perfectly logical. This boy hasn’t seen a squirrel before, but he has seen a dog. Presented with a new stimulus, he consulted his filing cabinet and pulled up the “dog schema.” Dogs, it says, are four-legged animals with fur and tails. When you put it like that, squirrels do resemble dogs.

Karsen: Wow, that is interesting. Would this be considered an example of assimilation?

Vincent: Yes. The author says that what's going on inside the child's mind when he misidentifies a squirrel is an example of assimilation. He is trying to impose his own structure on the environment. Like digestion, cognitive assimilation works the same way. The squirrel met all the criteria of the dog schema so the boy imposed this schema on this new stimulus, charting it onto his mental map of the world.

Assimilation is a quantitative process. As we assimilate more and more stimuli, our schemas cover more of our environment, allowing us to respond appropriately in more situations. This is one driver of cognitive development.

Karsen: But if he assimilated every four-legged animal to the dog schema, that organization of knowledge wouldn’t be very useful since he wouldn't be able to tell animals apart.

Vincent: That’s where accommodation comes in. Sometimes new stimuli don’t fit our existing schemas. On first sight, squirrels look like dogs; octopuses, however, do not. Assimilating squirrels into a dog schema won’t work either if the boy’s mother tells him that dogs are pets that live indoors and squirrels are wild animals that live outdoors.

There are two ways of accommodating new information and experiences. One is to create new schemas, like pets and wild animals. The other is to modify existing schema. For example, the boy could reorganize the dog schema as a mammal schema which includes both dogs and squirrels as subcategories.

Karsen: It seems like kids' curiosity is beneficial to their development.

Vincent: That's what the author says and I'd say so too. According to the author, there are two ways in which we respond to our environments. The first is an act directed outwards toward the world; the second is an act internalized as a thought.

Karsen: But when and why do these acts take place?

Vincent: According to Piaget, these acts are responses to needs. The feeling that something is missing determines the goal of your behavior. For example, when you feel cold, you seek what is missing: warmth. This is an example of the first kind of act. Your environment is cold and you need warmth.

Karsen: You identified the need but, how do you get that warmth?

Vincent: That's where your thoughts, the second kind of act, comes in. Cognition guides this behavior. For example, by providing schemas or knowledge you have, to locate a blanket or thermostat.

The ultimate goal is to create an equilibrium between the individual and their environment. And that is what the author claims will propel us through stages of cognitive development.

Karsen: What is equilibrium with your environment?

Vincent: Equilibrium is a state of harmonious balance between the individual and their environment. In this state, they can assimilate the things they encounter into existing schemas.

On the other hand, disequilibrium occurs when schemas cannot assimilate the stimuli in a person’s environment. This is a frustrating and disorienting state. The individual’s mental map no longer explains the world around them. Something or some knowledge is missing.

Karsen: What do you do if you reach disequilibrium?

Vincent: The author says that when assimilation fails, the individual must accommodate. In children, genuine intellectual breakthroughs are the fruit of accommodations. By creating new schemas capable of making sense of the environment, the individual restores equilibrium at a higher level. Now they can not only assimilate more information, they can also develop more complex behavioral responses. This state lasts as long as these new schemas continue to make sense of the world. Once they stop doing this, the process begins anew.

Karsen: So that little boy was doing great with his dog schema until he saw a squirrel and that threw off his equilibrium.

Vincent: Yep. And that lead to this process to reach equilibrium, resulting in him gaining more intelligence about animals. In Piaget’s terms, the individual develops a new psychological structure that provides new tools to solve new and increasingly complicated problems. Slowly but surely, they advance toward using the logic we associate with adult intelligence.

Karsen: That makes sense that over time you have more experiences where you take in new information but is there a timeline for how long this should take? For example, should parents worry about whether or not their child has certain schemas at certain ages?

Vincent: Well, Piaget’s experimental research led him to the conclusion that these breakthroughs could be divided into a series of milestones corresponding to discrete age brackets. It was on this basis that he formulated a theory of the various stages of cognitive development.

The first stage happens during the first 24 months of life, when infants start their remarkable journey of discovery. The newborn’s physical structure gives her ready-made sensorimotor functions to explore her world. They can perceive sights and smells and coordinate these perceptions with movements, or motor responses.

Karsen: But, aren't infants relatively helpless in the beginning of their lives?

Vincent: Thanks to these functions, they are far from helpless. Take innate skills like the sucking reflex. When a newborn’s lips are stimulated, they'll reflexively respond by making sucking movements. They also quickly learn from experience to distinguish between various stimuli. When hungry, they’ll reject the skin around their mother’s nipple and only suck at the nipple itself, suggesting an early form of recognition. The author says at the first stage of development, infants discover the existence of independent objects.

According to Piaget, infants lack a concept of the object, meaning that they do not understand that objects exist independently of actions such as looking, touching, and sucking. They only believe what they can perceive. The acquisition of this concept is, for him, the most important breakthrough of the sensorimotor stage of development.

Karsen: Is this like how if you hide a toy from an infant, they will forget it exists?

Vincent: Yes. For example, Karsen, if you put your keys in a drawer, you will know they will still be there several hours later even though you haven't seen or touched them. This is called decentering. Since you understand objects exist independently of yourself you can grasp higher concepts like cause and effect and reasoning. So if your keys aren't in the drawer, you assume someone moved them. This reasoning allows us to navigate the world effectively.

Karsen: Basically, for the first 24 months, it's the infants world, and we are all just objects living in it.

Vincent: Haha kind of. At least for the first 8 months. Piaget's research led him to believe that infants develop this independent object concept at around eight months. After 8 months, infants become hunters of hidden objects. The author took this as evidence that infants grasped the independent existence of objects. This is the first step towards decentered reason that defines adult intelligence.

Karsen: What's the next stage after that?

Vincent: The second stage of development lasts from age 2 to age 7. During this stage, children possess a concept of objects and begin exploring the relationships between things in their environment. The author calls this the preoperational stage. While children attempt to analyze how objects or ideas fit together, they don't yet have the ability to combine, separate or transform ideas logically.

Karsen: Why don't they have those abilities?

Vincent: As the author importantly notes, that's because children still haven't fully decentered their sense of self. They are egocentric in the preoperational stage of development. This means that they struggle to see the world from any perspective other than their own.

Karsen: So the world as they see it is still all about them. 2 years old to 7 years old seems like a wide range for one stage. Are there differences within this stage for different ages?

Vincent: There's an example in the book of a famous experiment Piaget conducted with children in this range. A cardboard mountain is placed in the middle of the table. First the child walks around the table to get the full view. Then the child stands still and the researcher moves a doll around the table. At certain points, the doll stops and “looks” at the mountain. The child is then shown a series of drawings representing different views of the mountain and asked to pick the drawing which best matches what the doll is seeing. At the preoperational stage, children almost always pick drawings that correspond with their view of the mountain.

Karsen: Because they understand the world from their view?

Vincent: Right. By contrast, seven- or eight-year-olds, complete this task fairly easily. Their spatial schema is decentered and differentiated.

In addition to object placement, this concept applies to time. When four- and five-year-old children watch two objects depart simultaneously from point A and arrive at two different places, points B and C, they struggle to reconstruct this sequence of events. While recognizing that one object came to a halt when the other one didn't, children this age still refuse to accept that both stopped “at the same time” – simply because they stopped at different places.

Karsen: So then around age 7, they begin to apply logic to things other than themselves?

Vincent: The third stage of cognitive development happens between ages 7 and 11. To answer your question, yes. They are able to apply logic to things other than themselves, but that is restricted to physical objects rather than abstract ideas, which is why Piaget termed this the concrete operational stage.

Karsen: What kind of logic do children use in this stage of development?

Vincent: According to the author, at this stage, children master the principles of conservation, reversibility, and classification. Conservation is the idea that something keeps its identity. So it remains the same even when its outward appearance changes. For example, a child at age 6 who hasn't learned conservation, is able to count 5 marbles laid out in a neat row. But, if the marbles are randomly spread across the table, they may tell you there are now more marbles. They cannot conserve number. This is the same if you pour water from a tall, thin glass into a short, wide glass, preoperational children believe the amount of water has changed.

Karsen: So they fail to conserve volume.

Vincent: Yes. But children between the ages of 7 and 11 can grasp this concept. Conservation is vital to another important concept in this stage which is reversibility. A child in this stage can understand that a ball of dough retains its identity whether you roll into a sphere, a long log, or ten small spheres. Because they learned to conserve substance, they understand that you can take a sphere, roll it into a log, and return it to its original state.

The last concept in this concrete observational stage is classification. To illustrate this the author give an example of an experiment. When Piaget showed preoperational children a collection of white and brown beads made from wood, they were unable to determine whether there were more wooden beads or more white beads. In the concrete operational stage, this problem becomes simple to solve.

Karsen: Why?

Vincent: Well, children now understand that white beads are a subcategory of a larger class, wooden beads. And they are able to apply this principle of classification more broadly.

Karsen: What about children older than 11 years old? What stage is this and how many stages are left?

Vincent: This is actually the last of Piaget's stages of development. Children 11 years old and older fall into Piaget’s formal operational stage. Unlike concrete operations, formal operations are not restricted to solving tangible problems like counting marbles on a tabletop – they can also be applied to abstract problems. A milestone of this period is using symbols to understand abstract concepts. Not only that, but older kids and adults can also think about multiple variables and come up with hypotheses based on previous knowledge.

Karsen: So thoughts are treated in the same way that objects were in the previous stages?

Vincent: Yes and they can be manipulated by the mind. Piaget believed that people of all ages developed intellectually. Once a person reaches the formal operational stage, it’s more about building upon knowledge, not changing how it’s acquired or understood. This is where deductive reasoning begins to be used to solve problems. Their brain uses "if" "then" statements based on things they know to learn new things. If these are true, it follows that the conclusion must also be true.

Karsen: How are symbols used in deductive reasoning?

Vincent: The book gives an example of the logic. A is bigger than B. That’s our first premise. Here’s the second: B is bigger than C. Deduction and conclusion: A is bigger than B and C. Because this form of reasoning applies to abstract problems, Piaget calls it hypothetical-deductive reasoning. Basically by using deductive reasoning, Piaget is saying that the structure of thinking is logical.

Karsen: So regardless of if deductive reasoning results in a correct answer or not, intelligence is shown by the ability to use it as a structure of logical thinking.

Vincent: Exactly. Another characteristic of this stage is working with false ideas. Say you present a preoperational child with a problem that assumes that coal is white. Usually, the child will claim that coal isn’t actually white but black, and will not be able to progress beyond this to solve the problem. Older children, by contrast, can assume a hypothesis they don’t believe, to be true for the purpose of the problem. For Piaget, the ability to think as if something were true is precisely the kind of reasoning critical to the work of philosophers and scientists.

Karsen: So basically development evolves from self to objects to thoughts. After this stage you basically can learn anything, right?

Vincent: Yes, after this, you have an endless ability to build upon the concrete knowledge you've acquired up till this stage.

Karsen: It sounds like the key takeaway from this title is that intelligence is active. To figure out how the world works, we have to poke at it – literally and then metaphorically. Some things we encounter can be understood in terms of what we already know; others can’t. If they can, we assimilate. If they can't, we accommodate. These processes are examples of intellectual adaptation to our environment. Understanding the different stages may help you better understand your child and assist their learning development.


Karsen: That’s it for your briefing. I’m Karsen Kolnicki.

Vincent: And I’m Vincent Phamvan.

Karsen: We’ll see you next time.


Think of developmental psychology, and the name of Jean Piaget immediately springs to mind. His theory of learning lies at the very heart of the modern understanding of the human learning process, and he is celebrated as the founding father of child psychology. A prolific writer, is the author of more than fifty books and several hundred articles. 

The Psychology of Intelligence is one of his most important works. Containing a complete synthesis of his thoughts on the mechanisms of intellectual development, it is an extraordinary volume by an extraordinary writer. Given his significance, it is hardly surprising that Psychology Today pronounced Piaget the Best Psychologist of the twentieth century.

Leave a Comment