Scientific study of change & continuity across the lifespan
Developmental psychology explores systematic, age-related changes in physical, cognitive, and socio-emotional domains from conception to late adulthood, emphasising both growth and decline.
Classic & contemporary models that organise lifespan findings
In-depth tables of age ranges, core conflicts, & hallmark achievements
Big idea : Children are little scientists who actively build mental models of the world. Development proceeds through four qualitatively different stages, each unlocking new logical operations that let the child think in increasingly abstract ways.
| Stage | Approx. Age | Key Attainments | Hallmark Tasks |
|---|---|---|---|
| Sensorimotor | 0 – 2 yrs | Object permanence, goal-directed actions | A-not-B task |
| Pre-operational | 2 – 7 yrs | Symbolic play, language explosion, egocentrism | Three-mountain task |
| Concrete Operational | 7 – 11 yrs | Conservation, decentration, class inclusion | Liquid & clay conservation tasks |
| Formal Operational | 12 yrs + | Abstract reasoning, hypothetico-deductive logic | Pendulum problem |
Children progress via assimilation() & accommodation(), constructing increasingly complex schemas.
Big idea : Personality evolves through eight lifespan “crises.” At each age we must balance two opposing forces (e.g. Trust ↔ Mistrust); successful resolution leaves us with a virtue (hope, will, purpose…) that fuels later growth.
| # | Conflict | Virtue Gained | Age Span |
|---|---|---|---|
| 1 | Trust vs Mistrust | Hope | 0 – 18 m |
| 2 | Autonomy vs Shame | Will | 18 m – 3 yrs |
| 3 | Initiative vs Guilt | Purpose | 3 – 5 yrs |
| 4 | Industry vs Inferiority | Competence | 6 – 11 yrs |
| 5 | Identity vs Role Confusion | Fidelity | 12 – 18 yrs |
| 6 | Intimacy vs Isolation | Love | 18 – 40 yrs |
| 7 | Generativity vs Stagnation | Care | 40 – 65 yrs |
| 8 | Integrity vs Despair | Wisdom | 65 yrs + |
Successful resolution produces a psychosocial virtue that scaffolds the next stage.
Big idea : Behaviour is driven by unconscious instinctual energy (libido). As this energy shifts to different body zones across childhood, we face conflicts; how we resolve them shapes adult personality traits.
| Stage | Age | Erogenous Focus | Fixation Outcome (if unresolved) |
|---|---|---|---|
| Oral | 0 – 18 m | Mouth, sucking | Oral-dependent habits (smoking, overeating) |
| Anal | 18 m – 3 yrs | Bladder & bowel control | Anal-retentive or expulsive traits |
| Phallic | 3 – 6 yrs | Genitals (Oedipal focus) | Vanity, recklessness |
| Latency | 6 – 12 yrs | Dormant libido | Difficulties with intimacy |
| Genital | 12 yrs + | Mature sexuality | Balanced personality |
Freud framed development as resolution of instinctual energy (libido) conflicts; modern views treat it as historical context.
Big idea : Moral judgment matures in three levels (pre-, conventional, post-) that reflect widening concern—from self-interest to societal rules to universal principles of justice. Progress depends on cognitive growth and social dialogue.
| Level | Stage | Reasoning Focus |
|---|---|---|
| Pre-conventional | 1. Obedience / Punishment | Avoid punishment |
| 2. Instrumental Relativist | Self-interest, rewards | |
| Conventional | 3. Interpersonal Concordance | “Good-boy/girl” approval |
| 4. Law & Order | Maintain social order | |
| Post-conventional | 5. Social Contract | Mutual benefit, rights |
| 6. Universal Ethical Principles | Abstract justice / conscience |
Progression is not strictly age-bound; few adults reach Stage 6. Moral judgment ≠ moral behaviour.
Big idea : Development is the product of ever-changing interactions (proximal processes) between a person and nested environmental systems—from family to culture to historical era.
Later PPCT revision emphasises Proximal Processes, Person, Context, Time. No discrete stages but shifts as nested contexts evolve.
Big idea : Learning is fundamentally social. Adults and peers “scaffold” the child within the Zone of Proximal Development, and external cultural tools (language, symbols) gradually become internal mental functions.
Development occurs through internalisation() of culturally mediated tools (language, symbols). The Zone of Proximal Development defines the gap between solo ability & guided potential. Staged change is fluid rather than discrete.
How developmental scientists generate evidence
Developmental psychologists rely on three complementary research strategies to describe and explain how people change over time:
Illustrative Example — Accelerated Longitudinal Study
Suppose you recruit three birth cohorts (children born in 2015, 2017, and
2019) and assess them annually for six years. Because the cohorts’ ages
overlap, you can map a nine-year developmental span (ages 6 to 14) in only
six years, while also checking whether each cohort follows the same or
different trajectories in cognition and pubertal-hormone levels.
Sequential designs combine the breadth of cross-sectional snapshots with the depth of longitudinal tracking, providing a powerful framework for separating age, cohort, and period influences in lifespan research.
Key physical, cognitive & socio-emotional changes
| Domain | 6 mo | 12 mo | 24 mo |
|---|---|---|---|
| Motor | Sits unaided | Crawls / cruises | Runs, climbs |
| Cognitive | Object permanence emerging | First words | Symbolic play |
| Social | Social smile | Joint attention | Self-recognition |
Milestones are averages—individual variability is expected.
Cross-cutting issues shaping modern development
OECD data show adolescents averaging 49 hrs/week on screens, linked to mental-health risks and cognitive inflexibility; policy recommends family media plans and tech-company accountability.
Developmental psychopathology frames ADHD, ASD, and learning disorders as variations in brain networks, advocating early intervention and strength-based supports.
WHO emphasises nurturing care (nutrition, security, responsive caregiving) during the first 1000 days to avert inter-generational inequality.