Understanding Developmental Psychology: From Research Methods to Piaget’s Stages

Name: Introduction to Developmental Psychology: Piaget’s Stages
Uploaded: 2026-01-20T16:56:18.813086+00:00
Channel: Professor Dave Explains
Description: Summary and key takeaways on Understanding Developmental Psychology: From Research Methods to Piaget’s Stages, covering Introduction Children are often

Professor Dave Explains

Jan 20, 2026

•

2 min read

YouTube video ID: eJTIo_MhG3M

Source: YouTube video by Professor Dave Explains — Watch original video

PDF

Introduction

Children are often described as sponges that soak up knowledge. Developmental psychology examines how thoughts, feelings, and behaviors evolve from infancy through adulthood, emphasizing the lasting impact of early experiences.

How Psychologists Study Development

Longitudinal studies – follow the same individuals over years (e.g., tracking moral reasoning from age 4 onward).
Cross‑sectional studies – compare different age groups at one point in time (e.g., morality of 4‑, 6‑, and 8‑year‑olds).
Age‑of‑onset studies – assess each age group separately without direct comparison.
Cohort (generational) studies – examine how people raised in different eras think about the same topic (Boomers vs. Millennials).

Nature vs. Nurture

The classic debate asks whether genetics (nature) or environment (nurture) shapes development. Modern consensus: both interact. Genes set potentials, while experiences can turn genes on or off, influencing behavior.

Children Are Not Mini‑Adults

Children occupy a distinct developmental niche.
Their reasoning, perception, and learning strategies differ fundamentally from adults.
Knowledge builds through active experimentation with the world.

Piaget’s Stages of Cognitive Development

1. Sensorimotor Stage (0‑2 years)

Learning through senses and motor actions.
Development of object permanence.
Cause‑and‑effect understanding (e.g., shaking a rattle).

2. Preoperational Stage (2‑7 years)

Rapid language acquisition.
Symbolic play (using objects to represent something else).
Difficulties with conservation and perspective‑taking.

3. Concrete Operational Stage (7‑11 years)

Mastery of conservation.
Emergence of logical thought, especially inductive reasoning.
Thinking remains tied to concrete, observable information.

4. Formal Operational Stage (12+ years)

Ability to reason abstractly and hypothetically.
Solve problems mentally without concrete objects.
Development of systematic, scientific thinking.

Modern Perspectives

Piaget’s sequence remains influential, but researchers acknowledge variability in timing.
Not all children progress at the same rate; faster progression does not equal higher intelligence.
The framework helps educators and clinicians understand typical cognitive milestones.

Looking Ahead

Developmental psychology covers many more topics—attachment, personality, social development—each building on the foundations discussed here.

Child development results from a continuous interaction between genetic predispositions and environmental experiences, and Piaget’s stages provide a valuable, though flexible, roadmap for understanding how children’s thinking evolves over time.

Frequently Asked Questions

Who is Professor Dave Explains on YouTube?

Professor Dave Explains is a YouTube channel that publishes videos on a range of topics. Browse more summaries from this channel below.

Does this page include the full transcript of the video?

Yes, the full transcript for this video is available on this page. Click 'Show transcript' in the sidebar to read it.

How Psychologists Study Development

- **Longitudinal studies** – follow the same individuals over years (e.g., tracking moral reasoning from age 4 onward). - **Cross‑sectional studies** – compare different age groups at one point in time (e.g., morality of 4‑, 6‑, and 8‑year‑olds). - **Age‑of‑onset studies** – assess each age group separately without direct comparison. - **Cohort (generational) studies** – examine how people raised in different eras think about the same topic (Boomers vs. Millennials).

Helpful resources related to this video

If you want to practice or explore the concepts discussed in the video, these commonly used tools may help.

The Whole-Brain Child Book Recommended

Integrates neuroscience and developmental psychology to help parents support emotional and cognitive growth; useful now for applying research‑based strategies to everyday parenting

Amazon →

Piaget Cognitive Development Book

Offers clear explanations of Piaget’s stages with examples; helps students and educators grasp core concepts of child cognition

Amazon →

Developmental Psychology Textbook

Comprehensive overview of research methods, nature‑nurture debates, and developmental theories; essential for anyone studying psychology today

Amazon →

Links may be affiliate links. We only include resources that are genuinely relevant to the topic.

Summarize another video

Full Transcript YouTube

Have you ever heard someone say that their 
child is like a sponge? Or perhaps comment  
on how quickly their kid is growing up? These 
phrases and others like them relate to how  
children seem to soak up knowledge and change 
rapidly over their first few years of life.  
Kids change a lot during childhood, and what 
happens during this time period can have a lasting  
impact on their behaviors in adulthood. The field 
of developmental psychology tries to explain  
how and why people’s thoughts, feelings, 
and behaviors change over their lifetime,  
with a particular emphasis on childhood, since 
this is when a lot of important changes occur,  
and these changes predict later adult psychology. 
Developmental psychology is an enormous topic that  
would be impossible to cover in a single video, 
so let’s simply hit some highlights for now. 
Let’s start with the basics. How do psychologists 
study development? Psychologists have a few  
different techniques to answer different 
questions. Let’s say you’re interested in  
the development of morality. How does it change 
across one’s lifetime, and when does it develop?  
To answer the first question, you would want to 
perform a longitudinal study and follow the same  
group of people as they grow up. You would take 
a group of young children, say four-year olds,  
and ask them what they think right and wrong 
means. Then you would bring them back into the  
lab every few years, ask them the same questions, 
and see how their answers change. If you cared  
less about how morality changes across development 
and more about when children develop morality,  
you would probably do a cross-sectional study 
or an age of onset study. For a cross-sectional  
study, you would take a few groups of kids at 
different ages and see how their behaviors differ.  
How does the morality of eight-year olds differ 
from that of six-year olds and from that of  
four-year olds? An age of onset study is similar 
in that you’re studying different age groups,  
but in this case, you don’t compare the age 
groups to each other. Instead, you ask what  
do four-year olds do in this morality task? What 
about six-year olds? What about eight-year olds?  
Finally, let’s pretend you’re interested 
in how growing up at different times  
might affect morality. You would do a 
generational, or cohort, study in this case,  
and ask how people who grew up in different 
times thought about morality. Do boomers  
have the same ideas about morality as 
millennials? If not, how are they different? 
Now that we have a basic understanding of how 
developmental psychologists tackle developmental  
questions, let’s talk about a debate you may 
have heard of: nature vs. nurture. This debate  
is about what has the biggest influence on child 
development. Is your development constrained by  
nature, where the genes you possess control your 
behavior and psychology? Or is your development  
more influenced by nurture, meaning everything 
else that could influence your behavior,  
like learned associations from experience, 
the social and cultural environment,  
or your interactions with other people? Well, 
the answer is… both! The idea of nature vs.  
nurture is a false dichotomy. We don’t have 
to pit nature and nurture against each other.  
Development is influenced by both your genes 
and the environment you’re in. In fact,  
your environment and social interactions 
can influence which genes are expressed  
and how they are expressed, ultimately affecting 
your behavior. While some behaviors may be more  
influenced by genetic factors than others, and 
vice versa, development as a whole is affected  
significantly by both nature, the genes you 
have, and nurture, the environment you’re in. 
Let’s move on to actually talking about kids and 
how they develop. An important thing to note is  
that children are not just really dumb adults. 
Children occupy a very specific developmental  
niche. The way they view and interact with 
the world is inherently different from adults,  
and will change as the child grows and 
develops. This means that kids think and  
reason differently than adults and will see the 
world in different ways. As a child grows, they  
build up their knowledge about the world through 
their experiences. They are actively experimenting  
with the world around them, and from the results, 
building an understanding of how the world works. 
To get a framework around this process, 
we are going to focus on a theory that  
is commonly used to describe child development 
known as “Piaget’s Stages.” Jean Piaget was a  
psychologist in the early 1900s who proposed a 
theory to describe how childrens’ intelligence  
grows and changes. His theory relies on the idea 
that cognitive abilities build upon one another.  
As we go through these stages, we will reference 
some approximate ages at which children go through  
a particular stage. Psychologists today generally 
think that all children go through these stages  
in this order and on average at these time 
periods, but there is some variation. Certain  
kids move through the stages faster than 
others, and these kids aren’t necessarily  
‘smarter’, it’s just some natural variation.
Let’s move through Piaget’s stages now. The first  
stage is called the sensorimotor stage, and this 
usually occurs between birth and two years old.  
This stage is characterized by an enormous amount 
of growth and learning. We all go from being an  
infant who is lightly interacting with their world 
through reflexes, to a toddler who is actively  
moving and exploring. Kids in this stage use the 
skills and abilities that they are born with,  
like looking, grasping, and listening, to explore 
their environment. They use their senses and motor  
abilities to learn through trial and error 
about the world around them. It’s during the  
sensorimotor stage that children begin to learn 
that their actions can cause specific reactions.  
For example, they might begin to realize that 
when they shake a rattle, it makes a pleasing  
sound. Or that pushing a light switch causes 
a light to turn on or off. They also might try  
to make different sounds to see if they can get a 
response from a caregiver. An important cognitive  
milestone in this stage is the development of 
object permanence. Very young infants do not have  
object permanence, that is, they don’t understand 
that objects continue to exist even when they  
can’t be seen or heard. This is why young infants 
will act surprised during a game of peek-a-boo.  
When you hide behind your hands, the infants 
believe that you are actually disappearing.  
Older infants that have developed object 
permanence will learn and understand that you  
continue to exist even when they can’t see you.
The next stage is the preoperational stage,  
which happens around two years old to seven years 
old. In this stage, children become proficient in  
language. They also begin to think symbolically, 
as you know if you’ve ever played pretend with  
a child. They can use an object to represent 
something else, like pretending a broom is a  
horse if they want to be riding a horse. Kids in 
this stage still struggle with some logical tasks,  
and often struggle with adopting the view of 
other people. They may think that everyone  
sees things as they see them. They also struggle 
with conservation. For example, say you have two  
identical containers with equal amounts of liquid. 
Then you pour the liquid from one container into a  
differently shaped cup, like a tall, thin cup or a 
short, wide cup. Even though the amount of liquid  
did not change, children will say that there is 
more liquid in whichever cup appears to be fuller. 
The third stage is the concrete operational 
stage, which takes place between around seven  
and eleven years old. Unlike in the previous 
stage, children now understand conservation.  
They know that breaking a candy bar into more 
pieces does not mean there is more candy.  
Children in this stage also begin to develop 
logical thought. Although they still tend to  
be very concrete in their thinking, children 
are beginning to excel at certain logical tasks  
like inductive logic. This means that they can go 
from a specific experience to a general principle.  
Say you notice that every time you’re around a 
cat, you get itchy eyes and a runny nose. Children  
who have mastered inductive logic would then be 
able to induce that you are allergic to cats. 
The fourth and final stage of Piaget’s stages is 
the formal operational stage, occurring when kids  
are around twelve years old and older. Children 
and young adults in this stage have the capacity  
for much more sophisticated thought. They can 
think about abstract and theoretical concepts, and  
can come up with creative solutions to problems 
using logic. In this stage, a child doesn’t need  
actual concrete objects to answer questions via 
trial and error. Instead, they can perform mental  
operations in the head using abstract terms. For 
example, kids at this stage can work through the  
following question in their head: “If you imagine 
something made up of two quantities, and the  
whole thing remains the same when one quantity is 
increased, what happens to the second quantity?” 
Piaget’s four stages help us understand how 
children develop cognitively across development.  
Importantly, Piaget didn’t think that kids develop 
by simply adding more knowledge to their brains  
as they grow up. Instead, the quality of how they 
think changes as they progress through the stages.  
A seven-year old thinks differently 
than they did at age two.  
Today, psychologists generally appreciate and 
accept Piaget’s stages, with some caveats. As we  
mentioned earlier, there is a lot of variation 
in how children develop. Not all children will  
move through these stages at the same times. 
Still, Piaget’s stages provide a useful framework  
for thinking about child development and 
they played a huge role in influencing  
the field of developmental psychology. His 
theory also helped psychologists realize  
that kids think differently than adults, and 
that they aren’t just smaller versions of adults. 
There’s a lot more we could say about 
different topics in developmental psychology,  
and perhaps later in the series we will 
go deeper with this fascinating subject.  
But for now we’re going to move on to the 
next topic in the series, personality.