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What is Piaget’s Theory of Development?

Jean Piaget proposed four stages of cognitive development. These stages help teachers assess and best serve students in the classroom. That is, if we can discern that a student is significantly over or under-developed with regard to their particular phase of development, we can seek out support for that child. We can also work with children who are in a transitional phase from one stage to the next. When we understand what their next stage is supposed to entail, we can help them master those skills or abilities.

The four stages are:

  • Sensorimotor 18-24 months
  • Preoperational 18 months to 2 years
  • Concrete Operational 7 years to age 11
  • Formal Operational approximately age 11 through the rest of life

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One key part of Piaget's theory of cognitive development is his emphasis on adaptation. That is, he saw that young people did not yet have the tools that were available to fully developed adults. Rather, children undergo a lengthy process in which they find moments of disequilibrium with their world but then apply old lessons, schema to Piaget, to assimilate the new information or situation.

  • Schema

    Piaget's cognitive theory posits schemas as the core of one's ability to build mental models of the world. As we develop, our schemas become more intricate, detailed, and numerous. We have schemas to help us navigate our lives. For instance, one's schema for commuting to work would involve things like starting and driving a car, boarding a train, navigating a route, and arriving at the destination. Within each of these basic stages we have sub-schema such as shifting gears, purchasing a ticket, reading a map, using alternate routes, etc.

    In a developmental context, we see that these schema begin as rudimentary and simple ideas that largely concern basic behaviors, shape, color, and perhaps smell. After approximately 18 months, we begin to see how various items work together to form complex systems, etc.

  • Assimilation

    This is a part of Piaget's all-important notion of adaptation. When we assimilate, we take new information, objects, or situations and apply them to preexisting schema to understand them. For instance, if one knows French but then finds themselves in Spain, they might see that Spanish has many similarities to French. Thus, they assimilate the two in order to navigate the new culture. We use assimilation all the time when we visit new restaurants, drive new cars, or even meet new people.

  • Accommodation

    Accommodation is another vital part of adaptation. In the example above, a traveler to Spain might rely on their knowledge of the French language to navigate the new culture. However, while French and Spanish have many things in common, they will still have to adapt their schema so that they can learn the nuances of Spanish. Similarly, game players change their strategies to meet the unique demands of a new opponent or game.

  • Equilibrium

    In Piaget's developmental theory, the need for equilibrium is what drives cognitive development. That is, when a person encounters a new situation that cannot be easily assimilated, disequilibrium occurs. This triggers frustration and other negative emotions until the new information can be accommodated/assimilated. Once a person adapts to the new situation, growth and development occur.

What Are the Four Stages?

Sensorimotor Stage

This first stage of development begins at birth and continues until 18-24 months. This pre-linguistic stage involves adaptation to the world of objects and simple motor skills. During the early months of this stage, infants are unaware that objects continue to exist when they are out of sight. Thus, a key moment of equilibrium is when they gain object permanence. From this point, children understand that a toy or other object will remain in a chest, for example.

At the same time, children must learn to navigate their environment by rolling over, crawling, and finally walking. At about the same time that they are beginning to walk, children expand on the abstract lessons of object permanence and begin to represent objects and ideas with language. Once a child can understand that food is still in the cupboard, she can ask for it. Thus begins the next stage.

Preoperational Stage

At approximately age 18 months to two years, a child enters the Preoperational Stage, which lasts until around age seven. This stage is characterized by the increasing ability to use language. Verbal skills progress at what may seem like a rapid pace. Imagination and abstract thinking progress at a fast clip as well, and their expressions become more and more mature as the need for equilibrium with adults and siblings drives increasing adaptation.

Growing children in this stage will notably lack strong logic skills. They might struggle with abstractions such as time, distance, and how to compare and contrast items. It is also difficult for children in this stage to solve problems mentally, and they must still rely on physical representations. Further, they will be incapable of seeing things through the eyes of another. Thus, younger children might often seem to behave cruelly towards their peers, animals, and even adults. This egocentrism does not last forever, thankfully.

Concrete Operational Stage

During this stage, which begins around age seven and lasts until age 11, children begin to implement operational thought. They can represent operations in their minds and solve problems for items or situations that are far removed from their physical space. Another important cognitive ability is what Piaget termed conservation. This is the ability to understand that an object might retain its quantitative values (mass, weight, etc.) even though it has changed its appearance. Thus, they can now grasp the idea that the same volume of water fills both a tall, skinny container and a short, squat cup.

Children also begin to loosen their bonds of egocentrism. They begin to see that their thoughts and feelings are their own and are not necessarily shared by others. They can also begin to see how others might experience an event and are more aware of external events and situations that don't necessarily involve them.

Formal Operational Stage

This is the final stage of Piaget's theory of cognitive development, and it lasts from approximately age 11 through the rest of life. This stage is characterized by the ability to think abstractly, create hypothetical situations, and then test those hypotheses. We begin to see how seemingly disparate concepts or objects relate to one another, and the world becomes one of increasing possibility.

Though this is Piaget's final stage of cognitive development, human cognition continues to mature and grow. That is because Piaget saw that, by this point in life, people generally have the core abilities they need to navigate the world. From age 11 onward, people continue to respond to the need for equilibrium and have the ability to adapt and grow.

How Can Teachers Use This?

Developmental theories are a large part of what drives a teacher's approach to the classroom. In fact, every teacher-prep program requires courses on childhood development so that teachers have an understanding of where their kids are or should be from a psychological view. Most of these theories focus on our emotional and social lives. One of the most popular theories of human development, the Ericksonian model, addresses cognition and information processing almost as an afterthought.

What makes Piaget's model stand out in the field is its specific attention to cognitive development. It focuses on how human beings process information and how that processing changes throughout a lifetime. In particular, his theory focuses on the mechanisms that help us adapt and learn new concepts or skills.

In the classroom, teachers can apply Piaget's notions of assimilation and accommodation when introducing new material. They can help students approach a new idea through the lens of what they have already learned. When they can achieve what Piaget called equilibrium, they can then move forward to again advance their knowledge.

One key element for teachers to be cognizant of is their students' particular age and relative development. Preschool teachers can look at Piaget's Sensorimotor Stage and help children learn to recognize simple shapes and colors.

Teachers who have classrooms for Preschoolers through approximately grade 2 should take a close look at the Preoperational Stage. It's important to note that children in this stage will not have a grasp of logic. Rather, their thoughts and behaviors will be egocentric and more intuitive. Teachers can thus put their lessons and student interactions in this context. Later in the stage, early childhood educators can integrate more abstract thinking, non-egocentric concepts, and advanced language skills. Some students will be able to adapt more quickly to the increasing complexity and can be encouraged to model their adaptive methods for their peers.

Teachers can approach the two later stages, Concrete Operational and Formal Operational, in much the same way. They can assess where their students are within the age-appropriate stage and then help them transition to the next. For older students in the final stage, teachers can build on the basic tools of adaptation and build lesson plans that ease the acquisition of new knowledge and skills.


No theory is without its criticisms. Piaget's theory of cognitive development is no stranger to detractors who find that it does not hold up to professional scrutiny from researchers or pure theoreticians. In particular, Piaget's theory is attacked based on his research, sample bias, and a seeming underestimation of children's abilities.

Many point to the fact that Piaget based his work on a very small sample size that included his own children and their peers. Not only is this a very small group from which little data could expect to be culled, but the children involved were also all from privileged backgrounds. Further, since Piaget didn't clearly define his variables, it is nearly impossible to replicate his study. For any study to be considered valid, it must be subject to easy replication.

The theory is also attacked because it allegedly underestimates how children actually learn. Where Piaget posited that children in the Preoperational Stage were egocentric and incapable of understanding the experiences of others, subsequent research has contradicted this. In fact, research has found that children as young as three are capable of non-egocentric thoughts and behaviors.

How Piaget’s Philosophy & Work Has Helped

While much of Piaget's work has not been successful in holding up to subsequent research, it still holds value for psychologists and teachers alike. His theories are still taught as part of a standard course in Human Development and he retains relevance, not completely due to his scientific strengths, but because of his importance as a pioneer.

Piaget broke important new ground in the field of human development. If he is to be remembered for any one thing, it is his focus on children as distinct from adults. Before his work and writing, psychology largely saw children as small adults. Though his conclusions might not hold as much water today, Piaget was able to identify that children passed through developmental stages on their way to processing information as adults. Further, his work showed that parents, teachers, and other community members need to acknowledge this developmental process to produce high-functioning adults.

His methodology, while not without significant flaws, was also groundbreaking. That is because he conducted in-depth interviews with his subjects. Previous researchers had not attempted this, and now subjects are frequently asked to describe and analyze their own thinking.

Learn more about Piaget vs Vygotsky vs Montessori

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