How Do We Develop Across the Lifespan?

Changing abilities, relationships, and goals in changing contexts.

Level: Introductory
Reading load: 11 core readings in 6 units
Prerequisites: No prior developmental psychology course is assumed. Familiarity with comparison groups and correlation is helpful; How to Read Psychological Science offers an introduction.
Last reviewed: September 2026

Introduction

A life is made of changes whose dates do not explain them. An infant crosses a room, a child begins to understand another person's mistake, an adolescent responds to a new social world, and an adult redistributes the hours of a day. Development asks how such changes become possible: which processes carry them forward, and under what conditions?

This path begins with frameworks for thinking about change across a life. It then examines early movement and learning, relationships and understanding other minds, the reach of developmental samples, an intervention in caregiving, adolescence, and adult motivation and emotion. Conceptual works supply questions to ask; empirical papers give those questions something concrete to work on.

As you move through the sequence, keep three distinctions in view: an age difference versus change within a person, a developmental pattern versus its explanation, and a result in a particular setting versus a claim about everyone. You do not need to master every statistical technique to identify the comparison on which an argument depends.

Unit 1 of 6

What counts as developmental change?

Begin by deciding what an explanation of development needs to accomplish. Baltes widens the lens to the entire lifespan and to gains, losses, and plasticity. Sameroff asks how changes in people and contexts become connected. Together they help turn ‘children grow up’ into questions that a study might answer.

For example, learning to walk changes where a child can go and whom they can approach. Use the two frameworks to ask what develops within the child, what opportunities change around them, and how those changes could influence one another over time.

Reading
1 of 11
Theoretical Propositions of Life-Span Developmental Psychology: On the Dynamics Between Growth and Decline
Baltes, P. B. (1987). Theoretical propositions of life-span developmental psychology: On the dynamics between growth and decline. Developmental Psychology, 23(5), 611–626. https://doi.org/10.1037/0012-1649.23.5.611
Foundational argument · Major synthesis · Moderate · Full work: 16 pages
Use Baltes to establish the syllabus’s central distinction between describing an age pattern and explaining development. Watch how gains and losses depend on the ability, context, and criterion being considered.
A question to consider. A skill becomes faster but less flexible with practice. How could this count as both a gain and a loss, and what would you measure?
Reading
2 of 11
A Unified Theory of Development: A Dialectic Integration of Nature and Nurture
Sameroff, A. (2010). A unified theory of development: A dialectic integration of nature and nurture. Child Development, 81(1), 6–22. https://doi.org/10.1111/j.1467-8624.2009.01378.x
Major synthesis · Foundational argument · Moderate · Full work: 17 pages
Add reciprocal influence to the lifespan framework. Trace how a person changes a context that subsequently changes the person; ask what must be measured repeatedly to investigate that transaction.
A question to consider. A child’s growing confidence changes how much independence caregivers allow. Sketch two rounds of the transaction and identify a possible alternative explanation.

Unit 2 of 6

How do new abilities emerge?

A new capacity can be studied through bodily change, opportunities for action, and learning from experience. The motor-development review connects these processes; the infant-learning experiment isolates a much narrower question. Compare what each kind of evidence contributes to a developmental explanation.

Reading
3 of 11
Motor Development: Embodied, Embedded, Enculturated, and Enabling
Adolph, K. E., & Hoch, J. E. (2019). Motor development: Embodied, embedded, enculturated, and enabling. Annual Review of Psychology, 70(1), 141–164. https://doi.org/10.1146/annurev-psych-010418-102836
Major synthesis · Accessible · Full work: 24 pages
Apply the transactional perspective to concrete changes in movement. Examine how bodies, surroundings, and caregiving practices jointly shape opportunities, then ask what would establish a cascade into another domain.
A question to consider. If walking and vocabulary increase together, what evidence would show that new movement opportunities contribute to language learning?
Reading
4 of 11
Statistical Learning by 8-Month-Old Infants
Saffran, J. R., Aslin, R. N., & Newport, E. L. (1996). Statistical learning by 8-month-old infants. Science, 274(5294), 1926–1928. https://doi.org/10.1126/science.274.5294.1926
Landmark empirical study · Moderate · Full work: 3 pages
Use the controlled speech stream to see how researchers make a learning mechanism testable. Compare this short-term demonstration with the broader developmental processes in Adolph and Hoch.
A question to consider. What does successful discrimination after brief exposure establish, and what additional evidence would connect it to the development of everyday language?

Unit 3 of 6

How do relationships and understanding of other people develop?

Social development involves both relationships and ways of understanding other people. Ainsworth and Bell examine behavior within a structured social situation. Wellman and colleagues compare the order of several kinds of social understanding across samples. Both require careful attention to what an observable response means.

Reading
5 of 11
Attachment, Exploration, and Separation: Illustrated by the Behavior of One-Year-Olds in a Strange Situation
Ainsworth, M. D. S., & Bell, S. M. (1970). Attachment, exploration, and separation: Illustrated by the behavior of one-year-olds in a strange situation. Child Development, 41(1), 49–67. https://doi.org/10.2307/1127388
Landmark empirical study · Methodological contribution · Moderate · Full work: 19 pages
Follow the changing relationship between exploration and proximity-seeking across the procedure. Use this example to distinguish behavior in one episode from an interpretation of an enduring relationship.
A question to consider. Why would a single count of crying be a weaker basis for understanding attachment than the pattern across separation and reunion?
Reading
6 of 11
Scaling of Theory-of-Mind Understandings in Chinese Children
Wellman, H. M., Fang, F., Liu, D., Zhu, L., & Liu, G. (2006). Scaling of theory-of-mind understandings in Chinese children. Psychological Science, 17(12), 1075–1081. https://doi.org/10.1111/j.1467-9280.2006.01830.x
Landmark empirical study · Moderate · Full work: 7 pages
Examine whether developmental variation concerns the speed of a sequence or its order. Compare the task-based inference here with the structured observation in Ainsworth and Bell, including whose experience each procedure captures.
A question to consider. If task order differs between samples, what would you need to learn before attributing that difference to particular cultural practices?

Unit 4 of 6

How do environments shape developmental possibilities?

Context matters both to development and to the evidence researchers collect. First examine the population boundaries of the field’s claims. Then study an intervention that changes caregiving conditions, distinguishing what random assignment establishes from what remains uncertain about mechanisms, timing, and generalization.

Reading
7 of 11
The Persistent Sampling Bias in Developmental Psychology: A Call to Action
Nielsen, M., Haun, D., Kärtner, J., & Legare, C. H. (2017). The persistent sampling bias in developmental psychology: A call to action. Journal of Experimental Child Psychology, 162, 31–38. https://doi.org/10.1016/j.jecp.2017.04.017
Critical reappraisal · Methodological contribution · Accessible · Full work: 8 pages
Return to the samples in the previous units and identify the scope of their claims. Use the audit to ask which settings are missing and why a missing comparison could matter to a theory.
A question to consider. Choose one earlier finding. What population or setting would provide an informative challenge to its proposed explanation, and why?
Reading
8 of 11
Cognitive Recovery in Socially Deprived Young Children
Nelson, C. A., III, Zeanah, C. H., Fox, N. A., Marshall, P. J., Smyke, A. T., & Guthrie, D. (2007). Cognitive recovery in socially deprived young children: The Bucharest Early Intervention Project. Science, 318(5858), 1937–1940. https://doi.org/10.1126/science.1143921
Landmark empirical study · Moderate · Full work: 4 pages
Connect Sameroff’s account of person–context transactions to an actual change in care. Separate the randomized intervention comparison, the nonrandomized community comparison, and the interpretation of placement timing.
A question to consider. Which result supports a benefit of the intervention, and why would it still be insufficient to establish a universal deadline for developmental recovery?

Unit 5 of 6

What changes during adolescence?

Adolescence brings changes in bodies, social opportunities, and motivational priorities. The review offers a framework for relating them to cognitive and neural development. Evaluate it as a proposal that generates questions about contexts and trajectories.

Reading
9 of 11
Understanding Adolescence as a Period of Social–Affective Engagement and Goal Flexibility
Crone, E. A., & Dahl, R. E. (2012). Understanding adolescence as a period of social–affective engagement and goal flexibility. Nature Reviews Neuroscience, 13(9), 636–650. https://doi.org/10.1038/nrn3313
Major synthesis · Foundational argument · Challenging · Full work: 15 pages
Connect the proposed model to the earlier distinction between developmental patterns and explanations. Use its context-sensitive predictions to think beyond a single age ranking of competence.
A question to consider. An adolescent persists on a difficult task with friends present but gives up sooner when alone. What would you compare before explaining this as a change in motivation, cognitive control, or the meaning of the situation?

Unit 6 of 6

How do goals and emotional lives change in adulthood?

Return to the lifespan perspective through a theory of changing goals and a longitudinal study of emotion. Ask whether chronological age, perceived time, or changing circumstances do the explanatory work. The final pairing also brings the distinction between differences across people and change within people into focus.

Reading
10 of 11
Taking Time Seriously: A Theory of Socioemotional Selectivity
Carstensen, L. L., Isaacowitz, D. M., & Charles, S. T. (1999). Taking time seriously: A theory of socioemotional selectivity. American Psychologist, 54(3), 165–181. https://doi.org/10.1037/0003-066X.54.3.165
Foundational argument · Major synthesis · Moderate · Full work: 17 pages
Use socioemotional selectivity theory to formulate a developmental prediction that does not simply say older people differ from younger people. Compare its emphasis on goals with the contextual account of adolescence.
A question to consider. How could a study distinguish the influence of perceived time remaining from that of chronological age?
Reading
11 of 11
Emotional Experience Improves With Age: Evidence Based on Over 10 Years of Experience Sampling
Carstensen, L. L., Turan, B., Scheibe, S., Ram, N., Ersner-Hershfield, H., Samanez-Larkin, G. R., Brooks, K. P., & Nesselroade, J. R. (2011). Emotional experience improves with age: Evidence based on over 10 years of experience sampling. Psychology and Aging, 26(1), 21–33. https://doi.org/10.1037/a0021285
Landmark empirical study · Moderate · Full work: 13 pages
Evaluate the longitudinal evidence alongside the motivational theory. Track what was measured repeatedly, who remained in the study, and whether the design directly tests the proposed explanation.
A question to consider. Which conclusion can this study support about emotional change, and which new measurement or intervention would be needed to explain why that change occurs?

Scope and omissions

This is a foundation in developmental reasoning across the lifespan, with selected examples of physical, cognitive, social, and emotional change. It is not a complete survey of every age or domain. Prenatal development, language acquisition beyond segmentation, schooling, moral development, puberty, midlife roles, cognitive aging, disability, and developmental psychopathology need deeper treatment. The examples also expose, without resolving, the field’s uneven cultural and socioeconomic coverage.

Historical frameworks appear because they pose useful questions, not because their age guarantees their correctness. The pathway combines theory, reviews, experiments, structured observation, a cultural comparison, an evidence audit, an intervention, and longitudinal research. The optional works extend those arguments without adding to the core sequence.

Synthesis

Development unfolds as capacities, experiences, relationships, and goals alter one another through time. A new ability can open an opportunity that changes what comes next; a changed context can redirect a life. Age places events in order, but cannot explain their course. Gains and losses may coexist, and the same visible pattern may arise through different processes.

Choose one change from the path: a new motor skill, an understanding of another mind, a response to caregiving, a shift in adolescent engagement, or a change in adult emotion. Describe what changed without explaining it yet. Then propose a mechanism, identify the relevant context, and state a comparison that could challenge your account.

Now specify the people and period to which your claim applies. Would evidence from different ages establish change within a person? Could selective participation or changing measures produce the pattern? What would an intervention establish, and which developmental processes would it leave unresolved? A persuasive developmental explanation needs these distinctions as well as a plausible story.

For a closer investigation of emerging abilities, continue with How Do Infants Build Knowledge and Skills?. It connects infant measures with accounts of knowledge, perceptual learning, action, and social experience.

For a complementary path into describing and measuring variation between people, explore Individual Differences. To revisit the logic of causal claims and measurement, return to How to Read Psychological Science.