Developmental Psychology: Domain Guide

Piaget's stages are easier to hold as limitations than as achievements. A preoperational child is not simply 'less advanced' — the child centres on one dimension at a time, cannot mentally reverse a transformation, and struggles to take another viewpoint. Those three limitations generate every classic failure attributed to the stage, including the conservation tasks. Learning the limitation lets you predict the child's answer, which is what most items ask for.

Every developmental design fails in its own characteristic way, and the failures are complementary. Comparing different ages at one time confounds age with generation. Following one group over time confounds age with the passage of history and loses exactly the participants who differ most. That complementarity is why sequential designs exist: they run several cohorts longitudinally so that the two explanations can be separated instead of argued about.

Attachment classification is a measurement rule, not a personality description. Almost every infant protests separation; what differentiates the categories is what happens when the caregiver returns — whether the child is comforted and resumes exploring, avoids contact, or seeks and simultaneously resists it. Items in this area are built on that distinction, and answering from the separation phase reliably produces the wrong category.

The domain is framed by three recurring questions. How much of development is inherited and how much is a product of experience — a question modern accounts answer with interaction rather than with a share. Whether change is gradual or arrives in qualitatively distinct stages, which is the difference between an information-processing account and a Piagetian one. And whether early experience fixes later outcomes — the stability-versus-change question, where the evidence usually supports openness rather than fixity outside genuinely critical windows.

Piaget's account describes four stages defined by what the child can and cannot yet do. In the sensorimotor period, from birth to about two, the infant knows the world through action and achieves object permanence, the understanding that a hidden object still exists. In the preoperational period, from about two to seven, symbolic thought and language flourish but reasoning is limited by centration on a single dimension, by an inability to mentally reverse a transformation, and by egocentrism, meaning difficulty taking another person's perspective rather than selfishness. In the concrete operational period, roughly seven to eleven, conservation, reversibility, and classification arrive but reasoning stays tied to concrete material. In the formal operational period, from around twelve, hypothetical and systematic abstract reasoning become possible. The engine of movement between stages is equilibration: assimilating new experience into existing schemas until the mismatch forces accommodation.

Vygotsky offers the standing alternative. Where Piaget saw a child discovering the world largely alone, Vygotsky saw development driven by interaction with more capable partners inside a zone of proximal development, with language moving from social speech to private speech to inner thought. The practical contrast the test uses is that Piaget treats instruction as effective only once the child is ready, while Vygotsky treats well-targeted instruction as what pulls development forward.

Erikson's psychosocial theory runs across the whole lifespan as eight crises, each named by its opposing outcomes: trust versus mistrust in infancy, autonomy versus shame and doubt in toddlerhood, initiative versus guilt in the preschool years, industry versus inferiority in the school years, identity versus role confusion in adolescence, intimacy versus isolation in young adulthood, generativity versus stagnation in middle adulthood, and integrity versus despair in late life. Freud's earlier psychosexual stages — oral, anal, phallic, latency, genital — are examinable mainly as a contrast: Erikson's stages are social and lifelong, Freud's are bodily and complete by adolescence.

Kohlberg's moral development is scored by the reasoning offered, never by the choice made. At the preconventional level the reasons are consequences to the self: avoiding punishment, then serving one's own interests through exchange. At the conventional level the reasons are social: earning approval, then upholding law and social order. At the postconventional level the reasons are principled: agreed social contracts that can be revised, then universal ethical principles that may override law. Two people who make opposite decisions can occupy the same level, and the same decision can be justified from any level — which is exactly what items in this area exploit. Gilligan's critique argued that the framework privileged an ethic of justice over an ethic of care.

Attachment and parenting supply the social half of the domain. Harlow's work with infant monkeys showed a preference for contact comfort over the wire figure that supplied food, which undercut the view that attachment is simply learned through feeding. Bowlby framed attachment as an evolved behavioural system, and Ainsworth's Strange Situation turned it into a measurement: securely attached infants use the caregiver as a base for exploration, are distressed at separation, and are readily comforted at reunion; avoidant infants show little reaction to either; resistant or ambivalent infants are highly distressed and then simultaneously seek and resist contact; and a fourth, disorganised pattern shows contradictory approach-and-avoid behaviour. Baumrind's parenting styles cross two dimensions — demands and responsiveness — into authoritative (high on both), authoritarian (high demands, low responsiveness), permissive (low demands, high responsiveness), and uninvolved (low on both). Temperament research adds the child's own contribution, with the easy, difficult, and slow-to-warm-up profiles, and the concept of goodness of fit between temperament and environment.

The physical and cognitive milestones are worth a compact list. Prenatal development runs germinal, embryonic, and fetal, with the embryonic period the most vulnerable to teratogens because that is when the major structures form. Newborn reflexes — rooting, sucking, grasping, the Moro startle — are present at birth and fade on schedule, and their persistence or absence is diagnostic. Language proceeds through cooing, babbling, first words near the end of the first year, and telegraphic two-word speech in the second. Theory of mind, tested by the false-belief task, typically arrives around four. In later life, fluid abilities decline while crystallised knowledge is retained, which is why an overall claim that 'intelligence declines with age' is almost always the wrong option.

Method is where developmental items become genuinely difficult, because age can never be randomly assigned. A cross-sectional design compares different age groups at one moment: it is fast, but any difference is confounded with cohort, because the older group also had a different education, nutrition, and technological environment. A longitudinal design follows one group over years: it removes the cohort confound within that group but introduces attrition, practice effects from repeated testing, and the possibility that the historical period rather than age produced the change. A cross-sequential design combines the two, following several cohorts over time so that age effects and cohort effects can be separated. And because developmental variables are almost never manipulated, causal language in an option is usually a signal to look for the design that would have licensed it and to notice that it is absent.