Week 11 · Chapter

Chapter 11 — Development Across the Lifespan

Introduction to Psychology Free sample edition

The module's primary reading · ~40–50 minutes · Objective 7 (describe cognitive, social, and emotional development across the lifespan and compare the major families of personality theory and their assessment), Objective 5 (compare the major models of learning and memory and apply them to everyday behavior, including why memory is reconstructive), Objective 6 (analyze higher mental processes (cognition, judgment and its biases, language, and intelligence) and the forces of motivation and emotion) · Read it first this week; the lecture, the slides, the tutorial, the quiz, and the Analysis Workshop all build on it.

In plain language

You were once a baby who thought a hidden toy had stopped existing, and one day you will be an older adult who knows more words than you do today. Development is the word psychologists use for those changes, and for the things that stay the same, from the first year of life to the last. This week you will follow how thinking grows in four steps, how a helper can stretch what a learner can do, and how a baby forms a deep bond, called attachment, with the people who care for it. You will also see how the big questions of a life, such as "who am I?", change from the teen years to old age. The goal is to read a child's puzzling answer, or a grandparent's sharp memory for facts, as a stage in a long story rather than as a mistake.

Why you already care about this

You hold your hands over your face, count to three, and pull them away. "Peekaboo!" A baby who is 1 year old squeals as if you had vanished and come back from nowhere. Now picture the same child at 4, watching you pour juice from a wide glass into a tall, thin one. She insists the tall glass has more. Ten years later, at 14, she argues with you about what would happen to basketball if everyone in the world were the same height.

Each of those moments is the same girl at a different point in a long journey, and you have probably seen all three. Something changed between the squeal and the argument, and it was not only how much she knew. The kind of thinking changed. Psychologists have studied that journey for decades. In 1958, Harry Harlow published his studies of what infant monkeys need besides food. In 1950, Erik Erikson laid out a set of challenges that run from infancy to old age. You will meet their answers this week and test each one on an everyday case.

By the end of this chapter you will be able to:

state the three big questions of development and explain why nature and nurture work together rather than compete;
put Piaget's four stages in order and place a child in a stage using the boundary ages of about 2, 7, and 11;
match each stage to its hallmark, from object permanence to abstract reasoning;
spot a zone of proximal development and the scaffolding that bridges it in a new case;
describe Harlow's contact-comfort finding and how the Strange Situation tells secure from insecure attachment;
place three of Erikson's psychosocial stages on the lifespan;
contrast fluid and crystallized intelligence and explain why development is lifelong.

Carry this sentence with you: a stage is a kind of thinking, not a birthday.

Where we are

Already covered: Weeks 1 and 2 built the "how do we know?" habit. Week 3 mapped the brain, Weeks 4 to 7 covered sensing, awareness, learning, and memory, Week 8 reviewed it all, and Weeks 9 and 10 covered how you think, speak, want, and feel.
This week: how people develop across the lifespan: thinking, relationships, and identity, from infancy to old age.
How they connect: Week 9's intelligence and language return as abilities that grow and change with age, and Week 6's learning returns as the help a skilled person gives a learner.
Where we're going next: Week 12, Personality, asks what makes each person's pattern of thinking, feeling, and behaving their own, and how much of it stays stable over a life.

Three earlier ideas you already know matter most this week. In Week 3 you met neuroplasticity, the brain's ability to change its connections in response to experience. That is one reason development never fully stops. In Week 6 you met shaping, reinforcing small steps toward a target behavior; this week's scaffolding works in a similar step-by-step way. In Week 9 you saw that language develops in a fixed order, babbling, then one-word speech, then two-word speech, then telegraphic speech, and that intelligence can be measured on a standardized scale. This week asks how those abilities change from childhood to old age.

1. Ask the three big questions: nature, continuity, and stability

Think of two cousins raised in the same city. One grows tall like her father; the other speaks two languages because his grandmother lives with the family. Height looks like biology, and a second language looks like experience. Yet even height depends on food, and learning any language depends on a brain built to learn one. That tangle is where developmental psychology starts.

Developmental psychology is the branch of psychology that studies how people change, and how they stay the same, in body, thinking, and social life from conception to old age.

Developmental psychologists keep returning to three big questions.

Nature and nurture. How much does inherited biology shape you, and how much does experience? The modern answer is that the question is badly framed as a contest.

Nature and nurture is the question of how inherited biology (nature) and experience and environment (nurture) shape development; the two always interact, so neither side wins a contest.

Language is a good case. Every typical baby is born ready to learn a language: that readiness is nature. Which language the baby learns, and how many words it hears at the dinner table, is nurture. Neither part works without the other.

Continuity vs. stages. Picture walking up a ramp. Each step is a little higher than the last, and there is no clear line between one part and the next. Now picture a staircase. You are on one step, and then you are on a different step.

Continuity vs. stages is the question of whether development is gradual and cumulative, like walking up a ramp, or happens in distinct steps that differ in kind, like climbing a staircase.

Height grows more like a ramp. Piaget, as you will see in Section 2, argued that thinking grows more like a staircase.

Stability vs. change. Were you a shy toddler? If so, are you a shy adult?

Stability vs. change is the question of whether a person's traits stay much the same across the lifespan or shift as the person grows older and meets new experiences.

The honest answer is "some of both." Next week you will see how personality researchers measure which traits stay steady. This week you will see abilities, such as reasoning speed and stored knowledge, that change in different directions across a life.

Pause and think. Choose one. Answer it in two or three sentences.

(a) Pick one of your own abilities, such as a sport, a language, or a skill at work, and describe the nature part and the nurture part of how you got it.

(b) Pick one trait of yours that has stayed much the same since childhood and one that has changed, and say what you think kept one stable and changed the other.

Misconception check. Students often think the nature–nurture question has a winner, as in "intelligence is 100% genes" or "kids are blank slates." It is tempting because the phrase "nature versus nurture" sounds like a match with a score. The cure is to look for the interaction in any example. A child's inherited traits affect how the child meets the world, and the world shapes how those traits develop. Ask "how do they work together here?" rather than "which one wins?"

2. Climb Piaget's staircase: four stages in one order

Jean Piaget spent years asking children questions and listening closely to their wrong answers. He noticed that children of similar ages made the same wrong answers, and that the errors changed as children grew. To Piaget, that meant children were not small adults who knew less. They were thinking in a different way.

Piaget described four stages of thinking. They always arrive in the same order, and no stage is skipped. You can use them like a map. A stage, in his theory, is a kind of thinking, not only an amount of knowledge.

The sensorimotor stage is Piaget's first stage, from birth to about age 2, in which a baby knows the world through the senses and through actions such as looking, grasping, and mouthing.
The preoperational stage is Piaget's second stage, from about age 2 to about age 7, in which a child uses words, images, and pretend play but cannot yet reason logically about changes such as pouring or spreading out.
The concrete operational stage is Piaget's third stage, from about age 7 to about age 11, in which a child conserves and reasons logically about real, concrete objects and events.
The formal operational stage is Piaget's fourth stage, from about age 11 onward, in which a person can reason about abstract ideas and hypothetical situations that do not exist.

In order: sensorimotor → preoperational → concrete operational → formal operational. This course uses the approximate boundary ages 2, 7, and 11. Other courses sometimes shift a boundary by about a year, so read every age as "about."

Worked example — how long is each step? Use the boundary ages to find how many years each stage with an upper boundary lasts.

Sensorimotor. It runs from birth (age 0) to about 2. The width is 2 − 0 = 2 years.
Preoperational. It runs from about 2 to about 7. The width is 7 − 2 = 5 years.
Concrete operational. It runs from about 7 to about 11. The width is 11 − 7 = 4 years.
Formal operational. It begins at about 11 and has no upper boundary, so it has no width to compute.

In words: preoperational is the longest of the three stages with an upper boundary, at about 5 years. That is 5 years versus 2 years for sensorimotor, so 5 ÷ 2 = 2.5 times as long. For you as a parent, a teacher, or a babysitter, that means the preoperational child is the one you will see most often. Formal operational thinking, once it arrives, continues through adulthood.

Worked example — the placement rule. To place a child, compare the child's age with the boundaries 2, 7, and 11. Younger than 2 means sensorimotor. Between 2 and 7 means preoperational. Between 7 and 11 means concrete operational. Older than 11 means formal operational. The next three sections apply that rule to four children.

Misconception check. Students often scramble the order, putting concrete operational before preoperational, or think a bright child can skip a stage. It is tempting because the names are long and similar. The cure is the meaning hidden in each name. "Pre-operational" means before logical operations, so it must come first. "Concrete" logic about real things comes next, and "formal," abstract logic comes last. One caveat: the boundary ages are approximate, and conventions differ by about a year at the edges. The order is the part you can count on.

3. Start with the senses: the sensorimotor stage and object permanence

Watch a baby in a high chair drop a spoon on the floor, look down, and laugh. Then she does it again, and again. She is not being difficult. She is running an experiment on how the world works, using her hands and eyes. That is how a sensorimotor mind learns: by doing and sensing.

The great achievement of this stage is a single idea that adults take for granted.

Object permanence is the understanding that an object or person still exists when it cannot be seen, heard, or touched; Piaget's hallmark achievement of the sensorimotor stage.

A very young baby who watches you hide a toy under a blanket may stop looking for it, as if it no longer exists. An older baby lifts the blanket. Object permanence is being built across the first two years.

Worked example — peekaboo, age 1. Place the baby you played peekaboo with.

Compare the age with the first boundary. The baby is 1 year old, and 1 is below 2.
Place the child. Below 2 means the sensorimotor stage.
Name the hallmark. The squeal when your face reappears shows object permanence still being built. For a baby who is not yet sure your face still exists behind your hands, its return is a real surprise.

In words: the 1-year-old playing peekaboo is in the sensorimotor stage, and the game is fun precisely because object permanence is still under construction.

Object permanence links to the memory you studied in Week 7. To keep looking for a hidden toy, a baby must hold some picture of the toy in mind after it disappears. A mind that can do that has taken a big step.

Misconception check. Students often place object permanence in the preoperational stage, because it seems like a "thinking" skill rather than a "sensing" one. It is tempting because preschoolers are the children we picture doing puzzles. The cure is the timeline. Object permanence is the hallmark of the first stage, built before age 2. By the time a child enters the preoperational stage, it is in place, and the new challenges are logic and point of view.

4. Meet the preschool mind: egocentrism and conservation

Call a 3-year-old on a video chat and ask, "What are you holding?" He may hold a drawing up to his own eyes and say, "This!" He can see it, so he assumes you can see it too. Nothing is wrong with him. He is thinking like a typical preoperational child.

The preoperational child you meet at a birthday party has gained a lot. She uses words to stand for things, pretends a box is a car, and tells stories. But two limits mark this stage.

Egocentrism is, in Piaget's theory, a young child's difficulty seeing a situation from another person's point of view, such as assuming that everyone sees what the child sees.

Egocentrism here is not selfishness. A preoperational child may be very kind. She has trouble taking a second viewpoint in her mind at the same time as her own. (In everyday speech "egocentric" can sound like an insult; in Piaget's theory it is a description of a stage.)

The second limit is about amounts.

Conservation is the understanding that an amount stays the same when only its shape or arrangement changes, such as juice poured into a taller glass or a row of coins spread apart.

Worked example — juice glasses, age 4. Place the child at your kitchen table.

Compare the age with the boundaries. The child is 4. Since 4 is between 2 and 7, she is in the preoperational stage.
Run the test. She watches you pour all the juice from a wide glass into a tall, thin one. Nothing is added or spilled.
Hear her answer. She says the tall glass holds more.
Name the hallmark. She judges by one feature she can see, the height of the juice, and cannot yet hold the change in width in mind at the same time. That is no conservation yet.

In words: the 4-year-old is in the preoperational stage, and her answer about the tall glass shows she does not yet conserve.

Pause and think. Choose one. Answer it in two or three sentences.

(a) Describe something a young child you know said or did that might show egocentrism, and explain why it fits Piaget's meaning rather than the everyday meaning of the word.

(b) Describe how you would set up a conservation test at home with objects other than juice, and say what a preoperational child would likely answer.

Misconception check. Students often think a preoperational child who fails the juice test "doesn't understand pouring" or "isn't paying attention." It is tempting because the answer seems careless to an adult. The cure is to notice that the child's answer is consistent: she reliably picks the taller glass. That steady pattern is what Piaget meant by a stage. The child is reasoning, but from one visible feature at a time.

5. Watch logic arrive: the concrete and formal operational stages

Line up two rows of coins on a table at a lemonade stand, five in each row, side by side. Ask an 8-year-old which row has more. "The same." Now spread one row out so it is longer and ask again. "Still the same. You only moved them." That small, confident shrug is a big step in thinking.

Worked example — rows of coins, age 8. Place the child at the lemonade stand.

Compare the age with the boundaries. The child is 8. Since 8 is between 7 and 11, he is in the concrete operational stage.
Run the test. One row of coins is spread apart; no coin is added or removed.
Hear his answer. He says both rows still hold the same number.
Name the hallmark. He conserves. He can hold two facts at once, longer row and wider gaps, and reason that they cancel out.

In words: the 8-year-old is in the concrete operational stage, and his answer about the spread-out row shows conservation.

The concrete operational child reasons logically, but mostly about real things he can see or picture. You can test this yourself. Ask him to sort his toy cars by size and color at once, and he can. Ask him what freedom is, and he may answer with a concrete example, such as "staying up late."

The fourth stage adds abstract and hypothetical reasoning: thinking about ideas, possibilities, and situations that do not exist.

Worked example — a what-if question, age 14. Place the teen you are debating.

Compare the age with the last boundary. The teen is 14, and 14 is above 11.
Place the teen. Above 11 means the formal operational stage.
Name the hallmark. Asked how sports would change if everyone were the same height, the teen reasons about a world that does not exist. She might argue that the rules would reward speed and passing over height. That is abstract, hypothetical reasoning.

In words: the 14-year-old is in the formal operational stage, and her answer to the what-if question shows reasoning about something that is not real.

Put the four children together and the tally is tidy: 4 children, 4 stages, 1 child per stage, in the canonical order sensorimotor → preoperational → concrete operational → formal operational.

The four children from this week's worked example, with each child's age, Piaget stage, and the hallmark the scene shows
Scene	Age (years)	Comparison with the boundaries	Stage	Hallmark shown
Peekaboo	1	below 2	Sensorimotor	Object permanence still being built
Juice glasses	4	between 2 and 7	Preoperational	No conservation yet
Rows of coins	8	between 7 and 11	Concrete operational	Conservation
A what-if question	14	above 11	Formal operational	Abstract, hypothetical reasoning

Misconception check. Students often credit abstract reasoning to the concrete operational stage, or assume every adult reasons formally about everything. It is tempting because 8-year-olds can be very logical. The cure is the word "concrete": logic about real, present things. Reasoning about what-ifs and abstract ideas is the formal operational hallmark, and it begins at about 11. A limitation worth knowing: reaching the formal operational stage means a person can reason abstractly, not that every adult does so all the time.

6. Add the helper: Vygotsky's zone of proximal development and scaffolding

Think about a 6-year-old learning to ride a bike in a park. On her own, she wobbles and falls. With training wheels and a parent's hand on the back of the seat, she rides all the way down the path. A few weeks later the hand lets go, then the training wheels come off, and she rides alone.

Piaget's children mostly discover the world on their own. Lev Vygotsky (1978) stressed something Piaget gave less weight to: much of what children learn, they learn with other people. A parent, a teacher, an older sibling, or a coworker can carry a learner further than the learner could go alone.

The zone of proximal development (ZPD) is Vygotsky's term for the gap between what a learner can do alone and what the learner can do with help from a more skilled person.
Scaffolding is temporary support a more skilled person gives a learner inside the zone of proximal development, such as training wheels or a worked example, removed step by step as the learner's skill grows.

Worked example — training wheels, age 6. Find her zone and her scaffolding.

What can she do alone? Not ride: she wobbles and falls.
What can she do with help? Ride the whole path, with training wheels and a hand on the seat.
Name the gap. The space between "falls alone" and "rides with help" is her zone of proximal development.
Name the support. The wheels and the hand are the scaffolding.
Watch it come down. As her balance improves, the hand lets go and then the wheels come off. Scaffolding is meant to be removed.

In words: riding is inside this child's ZPD, and the training wheels and the steadying hand are scaffolding that is taken away as she learns.

You meet scaffolding in your own classes. A worked example before the practice set is scaffolding: it carries you through the first problem so you can try the next one more on your own. That is why this course shows a full worked example before asking you to work one.

In practice (your tools). When you use an AI chatbot as a study helper this week, you can ask it to act as scaffolding rather than a replacement. Type a request such as "give me a hint, not the answer," and then remove the support yourself on the next problem.

Misconception check. Students often think the zone of proximal development is "anything a learner cannot do." It is tempting because the word "zone" sounds like a wide area. The cure is to look at both edges. A task the learner can already do alone is below the zone, and a task the learner cannot do even with help is above it. The ZPD is the middle band where help makes the difference. Scaffolding aimed above the zone does not work, and scaffolding that is never removed is not scaffolding anymore.

7. Ask what a baby needs: contact comfort and attachment

Imagine a toddler at a family gathering. Her father steps out of the room, and she cries and crawls toward the door. When he comes back, she reaches up, is held for a moment, and then wriggles down to play with her cousins. That reach toward one particular person is a bond psychologists can study.

Attachment is the strong emotional bond between an infant and a caregiver, shown when the infant seeks closeness to the caregiver and is upset by separation.

For a long time, many psychologists assumed babies attach to whoever feeds them. Harry Harlow tested that idea with infant monkeys (Harlow, 1958). Each young monkey had two surrogate "mothers": one made of bare wire that held the bottle, and one covered in soft cloth that did not. The monkeys spent most of their time clinging to the cloth mother. They went to the wire one to feed and came back to the cloth one for comfort.

Contact comfort is the soothing that comes from touching something soft and warm; Harlow's infant monkeys clung to a soft cloth surrogate mother rather than a wire one that held the bottle.

In words: food alone did not build the bond; touch and comfort mattered. One honesty note: Harlow raised these monkeys apart from their real mothers. His studies are taught today both for the finding and as an example of why research with animals now faces careful ethical review, the same kind of review you met in Week 2.

Mary Ainsworth turned attachment into something you could observe in a laboratory playroom. In her Strange Situation, a toddler and caregiver enter an unfamiliar room with toys. A stranger comes in, the caregiver leaves briefly, and later returns. Observers watch closely, especially at the reunion (Ainsworth et al., 1978).

The Strange Situation is Ainsworth's laboratory procedure that observes a toddler through brief separations from a caregiver, a stranger's approach, and reunions, in order to classify the toddler's attachment as secure or insecure.
Secure attachment is an attachment pattern in which a toddler explores while the caregiver is present, may be upset when the caregiver leaves, and is comforted and returns to play at the reunion.
Insecure attachment is an attachment pattern in which a toddler either clings and is hard to comfort at the reunion or seems indifferent and avoids the caregiver, rather than using the caregiver as a safe base.

Worked example — reading a reunion. Two toddlers go through the Strange Situation.

Toddler one. She plays while her caregiver is there, cries when the caregiver leaves, reaches up at the reunion, calms within a moment, and goes back to the toys. Comforted and back to play: secure attachment.
Toddler two. He barely looks up when his caregiver leaves, and at the reunion he turns away and keeps playing alone. Avoiding the caregiver: insecure attachment.

In words: the Strange Situation reads attachment from what a toddler does at the reunion, not from how loudly the toddler cries at the separation.

Notice how Ainsworth turned a fuzzy word, "attachment," into an operational definition, a set of observable behaviors in a fixed procedure. That is Week 2's method at work.

Misconception check. Students often think the toddler who cries hardest when the caregiver leaves must be the insecure one. It is tempting because crying looks like distress. The cure is to watch the reunion. A securely attached toddler may cry at the separation and still be comforted quickly when the caregiver returns. The key behavior is what happens when the caregiver comes back.

8. Stretch development across a life: Erikson's psychosocial stages

Piaget's stages end at about age 11, with formal reasoning. But a 30-year-old starting a new career, or a 75-year-old looking at old photographs, is still developing. Erik Erikson (1950) wanted a map of the whole life.

Psychosocial stages are Erikson's eight stages of development from infancy to old age, each centered on one social and emotional challenge, written as a healthy outcome versus an unhealthy one.

Each stage name has two parts joined by "vs.": the healthy outcome comes first and the unhealthy one second. Three stages anchor the lifespan.

Trust vs. mistrust is Erikson's first psychosocial stage, in infancy, in which a baby whose needs are met reliably learns that the world is safe and that people can be counted on.
Identity vs. role confusion is Erikson's psychosocial stage of adolescence, in which a teenager tries out roles and values in order to form a stable sense of who they are.
Integrity vs. despair is Erikson's final psychosocial stage, in late adulthood, in which a person looks back on life and feels either that it was meaningful or that it was wasted.

Worked example — placing three people. Name the challenge you see in each life.

A baby whose cries bring a caregiver every night. Infancy, and the challenge is whether the world can be counted on: trust vs. mistrust.
A high school junior who joins the robotics team, quits it for theater, and argues with family about values. Adolescence, and the challenge is who to become: identity vs. role confusion.
A retired bus driver who tells her grandchildren which choices she is proud of. Late adulthood, and the challenge is whether life added up: integrity vs. despair.

In words: Erikson names the challenge each period of life brings, and the same person meets a new one in each period.

Pause and think. Choose one. Answer it in two or three sentences.

(a) Describe a choice you or someone you know made while trying out different roles or values, and explain how it fits identity vs. role confusion.

(b) Describe how an older adult you know talks about the past, and explain whether it sounds more like integrity or more like despair, and why.

Misconception check. Students often think Erikson's stages are pass-or-fail tests, so a baby who misses some care in infancy is doomed to mistrust for life. It is tempting because each stage is written as a pair of opposites. The cure is that Erikson described a balance in each stage, and later relationships and experiences can shift it. A caveat: Erikson's stages are a descriptive map of life's challenges, not a precise timetable with exact ages.

9. Finish with adolescence and aging: identity, fluid and crystallized intelligence

A 16-year-old changes her style three times in a school year. A 70-year-old crossword champion fills in rare words in seconds but takes longer than his grandson to learn a new phone game. Both are developing, in different directions.

Adolescence is the period of life from puberty to independent adulthood, marked by rapid physical change and by the search for a stable personal identity.
Identity is a person's stable sense of self: the values, roles, and commitments a person recognizes as their own.

Trying on styles, friends, and opinions is part of how a teenager finds out which ones fit. You may remember doing it yourself. That is Erikson's identity vs. role confusion at work.

Aging brings its own change, and it is not a simple decline, as you may have seen in your own family. Recall Week 9: intelligence is more than one number. Psychologists split one part of it into two kinds that age differently (Horn & Cattell, 1967).

Fluid intelligence is the ability to reason quickly and solve new problems that do not depend on what a person already knows; it tends to decline in later adulthood.
Crystallized intelligence is the knowledge, vocabulary, and skills a person has built up over a lifetime of experience; it tends to hold steady or grow in later adulthood.

Worked example — the crossword champion. Sort his two results.

Fast reasoning on something new. Learning an unfamiliar phone game takes him longer than it once did. That is fluid intelligence, which tends to decline in later adulthood.
Stored knowledge. Rare crossword words come to him instantly. That is crystallized intelligence, which holds steady.

In words: the same older adult can be slower on a brand-new puzzle and sharper on stored knowledge, because the two kinds of intelligence age differently.

This is one reason an experienced nurse, mechanic, or teacher can outperform a quicker newcomer. Years of crystallized knowledge often make up for a slower start on something new. Development is lifelong: change continues from the first year to the last, through both loss and gain.

Misconception check. Students often think intelligence goes downhill with age, so older adults are less capable across the board. It is tempting because slower reaction times are easy to notice. The cure is the split: fluid intelligence tends to decline in later adulthood, but crystallized intelligence holds steady. An older adult's vocabulary and know-how can keep growing long after reaction speed has peaked.

Key terms

Developmental psychology — The branch of psychology that studies how people change, and how they stay the same, in body, thinking, and social life from conception to old age. (first used: 1. Ask the three big questions: nature, continuity, and stability)
Nature and nurture — The question of how inherited biology (nature) and experience and environment (nurture) shape development; the two always interact, so neither side wins a contest. (first used: 1. Ask the three big questions: nature, continuity, and stability)
Continuity vs. stages — The question of whether development is gradual and cumulative, like walking up a ramp, or happens in distinct steps that differ in kind, like climbing a staircase. (first used: 1. Ask the three big questions: nature, continuity, and stability)
Stability vs. change — The question of whether a person's traits stay much the same across the lifespan or shift as the person grows older and meets new experiences. (first used: 1. Ask the three big questions: nature, continuity, and stability)
Sensorimotor stage — Piaget's first stage, from birth to about age 2, in which a baby knows the world through the senses and through actions such as looking, grasping, and mouthing. (first used: 2. Climb Piaget's staircase: four stages in one order)
Preoperational stage — Piaget's second stage, from about age 2 to about age 7, in which a child uses words, images, and pretend play but cannot yet reason logically about changes such as pouring or spreading out. (first used: 2. Climb Piaget's staircase: four stages in one order)
Concrete operational stage — Piaget's third stage, from about age 7 to about age 11, in which a child conserves and reasons logically about real, concrete objects and events. (first used: 2. Climb Piaget's staircase: four stages in one order)
Formal operational stage — Piaget's fourth stage, from about age 11 onward, in which a person can reason about abstract ideas and hypothetical situations that do not exist. (first used: 2. Climb Piaget's staircase: four stages in one order)
Object permanence — The understanding that an object or person still exists when it cannot be seen, heard, or touched; Piaget's hallmark achievement of the sensorimotor stage. (first used: 3. Start with the senses: the sensorimotor stage and object permanence)
Egocentrism — In Piaget's theory, a young child's difficulty seeing a situation from another person's point of view, such as assuming that everyone sees what the child sees. (first used: 4. Meet the preschool mind: egocentrism and conservation)
Conservation — The understanding that an amount stays the same when only its shape or arrangement changes, such as juice poured into a taller glass or a row of coins spread apart. (first used: 4. Meet the preschool mind: egocentrism and conservation)
Zone of proximal development (ZPD) — Vygotsky's term for the gap between what a learner can do alone and what the learner can do with help from a more skilled person. (first used: 6. Add the helper: Vygotsky's zone of proximal development and scaffolding)
Scaffolding — Temporary support a more skilled person gives a learner inside the zone of proximal development, such as training wheels or a worked example, removed step by step as the learner's skill grows. (first used: 6. Add the helper: Vygotsky's zone of proximal development and scaffolding)
Attachment — The strong emotional bond between an infant and a caregiver, shown when the infant seeks closeness to the caregiver and is upset by separation. (first used: 7. Ask what a baby needs: contact comfort and attachment)
Contact comfort — The soothing that comes from touching something soft and warm; Harlow's infant monkeys clung to a soft cloth surrogate mother rather than a wire one that held the bottle. (first used: 7. Ask what a baby needs: contact comfort and attachment)
Strange Situation — Ainsworth's laboratory procedure that observes a toddler through brief separations from a caregiver, a stranger's approach, and reunions, in order to classify the toddler's attachment as secure or insecure. (first used: 7. Ask what a baby needs: contact comfort and attachment)
Secure attachment — An attachment pattern in which a toddler explores while the caregiver is present, may be upset when the caregiver leaves, and is comforted and returns to play at the reunion. (first used: 7. Ask what a baby needs: contact comfort and attachment)
Insecure attachment — An attachment pattern in which a toddler either clings and is hard to comfort at the reunion or seems indifferent and avoids the caregiver, rather than using the caregiver as a safe base. (first used: 7. Ask what a baby needs: contact comfort and attachment)
Psychosocial stages — Erikson's eight stages of development from infancy to old age, each centered on one social and emotional challenge, written as a healthy outcome versus an unhealthy one. (first used: 8. Stretch development across a life: Erikson's psychosocial stages)
Trust vs. mistrust — Erikson's first psychosocial stage, in infancy, in which a baby whose needs are met reliably learns that the world is safe and that people can be counted on. (first used: 8. Stretch development across a life: Erikson's psychosocial stages)
Identity vs. role confusion — Erikson's psychosocial stage of adolescence, in which a teenager tries out roles and values in order to form a stable sense of who they are. (first used: 8. Stretch development across a life: Erikson's psychosocial stages)
Integrity vs. despair — Erikson's final psychosocial stage, in late adulthood, in which a person looks back on life and feels either that it was meaningful or that it was wasted. (first used: 8. Stretch development across a life: Erikson's psychosocial stages)
Adolescence — The period of life from puberty to independent adulthood, marked by rapid physical change and by the search for a stable personal identity. (first used: 9. Finish with adolescence and aging: identity, fluid and crystallized intelligence)
Identity — A person's stable sense of self: the values, roles, and commitments a person recognizes as their own. (first used: 9. Finish with adolescence and aging: identity, fluid and crystallized intelligence)
Fluid intelligence — The ability to reason quickly and solve new problems that do not depend on what a person already knows; it tends to decline in later adulthood. (first used: 9. Finish with adolescence and aging: identity, fluid and crystallized intelligence)
Crystallized intelligence — The knowledge, vocabulary, and skills a person has built up over a lifetime of experience; it tends to hold steady or grow in later adulthood. (first used: 9. Finish with adolescence and aging: identity, fluid and crystallized intelligence)

Summary

Development is change and stability across the whole lifespan.
Nature and nurture always interact; neither one wins a contest.
Continuity is a ramp; stages are a staircase.
Piaget's four stages run sensorimotor, preoperational, concrete operational, formal operational, at about 2, 7, and 11.
A stage is a kind of thinking, not a birthday.
Sensorimotor: object permanence is built before about 2.
Preoperational: egocentrism and no conservation yet; pour juice into a thin glass and the child says it holds more.
Concrete operational: conservation and logic about real things.
Formal operational: abstract, hypothetical reasoning from about 11.
The zone of proximal development is the gap help can bridge; scaffolding is removed as skill grows.
Harlow's monkeys chose contact comfort over food.
The Strange Situation reads attachment at the reunion: secure or insecure.
Erikson: trust vs. mistrust, identity vs. role confusion, integrity vs. despair, in that order across life.
Fluid intelligence tends to decline in later adulthood; crystallized intelligence holds steady.

Check your understanding

Work these before looking at the answers — they are ungraded, and the answers (with reasoning) are at the bottom of the page.

Marisol, who is 5, watches her uncle roll a ball of clay into a long snake. She says the snake has more clay than the ball did. Place Marisol in a Piaget stage using the boundary ages, and name the hallmark her answer shows.
A new cashier, Tomasz, cannot yet close out the register alone. With a coworker reading the steps aloud, he does it correctly. Name his zone of proximal development, name the scaffolding, and say what should happen to the scaffolding over the next few shifts.
Two toddlers in a Strange Situation both cry hard when their caregivers leave. At the reunion, Ife reaches up, calms quickly, and returns to the toys; Noor keeps crying, clings, and cannot be soothed for a long time. Which toddler shows secure attachment, and why does the crying at the separation not decide the answer?
A 68-year-old retired librarian, Priya, beats her nephew at a vocabulary game but takes longer than he does to solve a brand-new logic puzzle. Which kind of intelligence explains each result, and which Erikson stage is she most likely in?

Answers (worked reasoning — read after attempting)

Marisol is 5, and 5 is between 2 and 7, so she is in the preoperational stage. Rolling the ball into a snake changes only its shape; no clay is added or removed. Her answer shows she judges by one visible feature, the length, and does not yet conserve. A child in the concrete operational stage would say the amount is the same.
Closing the register is in Tomasz's zone of proximal development: he cannot do it alone, but he can do it with help. The coworker reading the steps aloud is the scaffolding. Over the next few shifts the coworker should read fewer steps, then only answer questions, and then step back, so the support is removed as his skill grows.
Ife shows secure attachment. The Strange Situation reads attachment mostly from the reunion, not the separation. A securely attached toddler may cry when the caregiver leaves and still be comforted quickly on return. Noor's clinging and inability to be soothed at the reunion fit insecure attachment, even though both cried the same at the separation.
Her vocabulary win reflects crystallized intelligence, knowledge built over a lifetime, which holds steady in later adulthood. Her slower time on a brand-new logic puzzle reflects fluid intelligence, fast reasoning on new problems, which tends to decline. At 68 she is in late adulthood, so she is most likely in Erikson's integrity vs. despair stage.

Next up in this module: the Readings & Resources page, the lecture tutorial, the practice set, and the quiz — and next week the Big Five trait model describes the stable patterns that make each person who they are.

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