What are Piaget's stages of cognitive development?

The sensorimotor stage, which starts at birth and lasts until the time our child is about 2 years old, is characterized by experiences gathered primarily through sensory stimuli and motor activities (hence the name). Basically, the sensorimotor child gets most of her input through moving about and observing what's going on around her.

There are six substages in the sensorimotor stage, and each is a small incremental step toward greater awareness and participation. At first, everything is pretty much a reflexive reaction to whatever is going on. But as soon as schemata (linked sets of perceptions, ideas and actions) are under construction, she begins to have more meaningful interactions with the world.

To understand schemata, let's take a step back for a second and look a little more closely at some of the fundamental elements of Piaget's theory. Piaget said that as people are exposed to new experiences and stimuli from the external world, they seek to return their minds to a state of equilibrium by settling the new knowledge internally in a place that makes sense.

We do this with the help of two main adaptive tools that work hand-in-hand: assimilation and accommodation. Assimilation is when we fit new information into an existing schema, and accommodation is when we change or create a schema because putting the new information anywhere else doesn't make sense. Thus we have used adaptation and organization to further cognitive development, and over time, our internal mental structures become increasingly complex.

But back to our baby girl. Gradually, she grasps the idea that she can use movement to accomplish things and produce results -- this is when rattles and car keys start to get really interesting -- and so she begins to act intentionally. Also, she catches on that things still exist even when little baby isn't there to look at them; a concept called object permanence. This is what makes peek-a-boo such a fascinating game to a very young child.

Once she starts chattering away, she's moved into the second phase, which we'll read about on the next page.

Once our child reaches about 2 years of age, she enters the second stage of development: the preoperational stage. She starts to really get a grasp on language, and to a certain extent, on symbols: She understands that objects can be identified by words and images, even when those objects aren't around. Memory and imagination gear up in tandem with this understanding of language and symbols, something which usually leads to extensive pretend play. Since she's still a little limited in her own experiences, such play often takes the form of role-playing scenarios imitating the actions of others. This symbolic play lets her understand more about what other people are doing around her.

However, she's still a bit simpleminded when it comes to separating things into categories. Seeing that an object can have more than one basic dimension to it at the same time is a challenge. Take playing with blocks. She wants all the blue blocks to be pushed into a pile together regardless of shape, but that causes a bit of a row with her play date, who pitches a fit because she wants all the circular blocks with the other circular blocks and the square blocks with the other square blocks, never mind what color they are. Each girl only sees the characteristic she cares about.

As you can see in the case of the argument over the blocks, children also tend to be bit egocentric at this stage -- that's because they aren't yet able to see things from other people's point of view. It stems from the fact that they've just begun to identify themselves as a person, separate and independent from the rest of the world, which consequently causes them to be very self-centered.

While our kid starts developing some intuitive logic, especially after age 4, she's still characteristically illogical in how she consciously perceives the world. We'll get into some of the areas in which our little test subject has to develop on the next page.

When our child gets to be around 7 years old, she enters the concrete operational stage, expands her skill set and starts to gain a much greater command over language. As her cognition develops, she also gets a better handle on conscious logic when it comes to objects and events; she does, however, still have trouble with abstract thought. She also gets a lot less egocentric (thankfully -- we've been waiting for this to finally kick in!), and starts to understand that other people don't necessarily see things from her same point of view.

As she gets older, she starts to grasp what Piaget called conservation, and can see that objects don't always alter in terms of their fundamental existence even when a physical aspect about them changes. That is, using one of Piaget's experiments as an example, she realizes that when fluid in two identical glasses is poured into two separate containers of different shapes, there is still the same amount of fluid in each of the new containers.

There are several attributes of conservation, including number, substance, mass, volume and weight. She'll master these concepts at different times throughout this stage, realizing that things can have more than one dimension at the same time. She learns how to classify (group) and serialize (order) things as well. She can manage basic problem solving and understand that things can be reversed into their basic components and vice versa.

Kudos, kiddo. You're getting there. One last stage to go.

Hooray! Our child has reached the fourth stage in Piaget's theory, the formal operational stage. Now at about 11, she's mastering the final milestones in cognitive development. She has a full command of logic, and she's even able to manipulate abstract concepts in her mind. Hypothetical and ideological notions have started to take hold, so perhaps our little lady has taken a crack at contemplating the size of the universe or considering the trolley problem. She's also better at reflecting on the future, so maybe she's starting to think seriously about what she wants to do when she grows up.

Additional abilities are added to her cognitive skill set, such as:

There might be a brief shift back into egocentrism with a touch of idealism early on in this stage, but hey, that's puberty for you.

So now she's all grown-up and ready to dive into the world with her head screwed on straight. It's important to note, however, that it's likely not all of her peers managed this final leap. Studies have found that some 30 to 35 percent of people never make it to this last stage [sources: Huitt, Epstein]. So let's not take our girl's accomplishment for granted!

On the next page, you can consider some logic problems of your own -- from the psychological changes that happen during pregnancy to those that happen when you're lost in the woods, with the little dilemma of quantum suicide thrown in for good measure.