sandwich generation The generation of middle-aged people who are supposedly “squeezed” by the needs of the younger and older members of their families. In reality, some adults do feel pressured by these obligations, but most are not burdened by them, either because they enjoy fulfilling them or because they choose to take on only some of them or none of them.

scaffolding Temporary support that is tailored to a learner’s needs and abilities and aimed at helping the learner master the next task in a given learning process.

science of human development The science that seeks to understand how and why people of all ages and circumstances change or remain the same over time.

scientific method A way to answer questions that requires empirical research and data-based conclusions.

scientific observation A method of testing a hypothesis by unobtrusively watching and recording participants’ behavior in a systematic and objective manner in a natural setting or in a laboratory; a search of archival data is another way to conduct scientific observation.

Seattle Longitudinal Study The first cross-sequential study of adult intelligence. This study began in 1956 and is repeated every 7 years.

secondary aging The specific physical illnesses or conditions that become more common with aging but are caused by health habits, genes, and other influences that vary from person to person.

secondary circular reactions The second of three types of feedback loops in sensorimotor intelligence, this one involving people and objects. Infants respond to other people, to toys, and to any other object they can touch or move.

secondary education Literally, the period after primary education (elementary or grade school) and before tertiary education (college). It usually occurs from about ages 12 to 18, although there is some variation by school and by nation.

secondary prevention Actions that avert harm in a high-risk situation, such as stopping a car before it hits a pedestrian.

secondary sex characteristics Physical traits that are not directly involved in reproduction but that indicate sexual maturity, such as a man’s beard and a woman’s breasts.

secular trend The long-term upward or downward direction of a certain set of statistical measurements, as opposed to a smaller, shorter cyclical variation. As an example, over the last two centuries, because of improved nutrition and medical care, children have tended to reach their adult height earlier and their adult height has increased.

secure attachment A relationship in which an infant obtains both comfort and confidence from the presence of his or her caregiver.

selective adaptation The process by which living creatures (including people) adjust to their environment. Genes that enhance survival and reproductive ability are selected, over the generations, to become more prevalent.

selective attention The ability to concentrate on some stimuli while ignoring others.

selective optimization with compensation The theory, developed by Paul and Margaret Baltes, that people try to maintain a balance in their lives by looking for the best way to compensate for physical and cognitive losses and to become more proficient in activities they can already do well.

self theories Theories of late adulthood that emphasize the core self, or the search to maintain one’s integrity and identity.

self-actualization The final stage in Maslow’s hierarchy of needs, characterized by aesthetic, creative, philosophical, and spiritual understanding.

self-awareness A person’s realization that he or she is a distinct individual whose body, mind, and actions are separate from those of other people.

self-concept A person’s understanding of who he or she is, in relation to self-esteem, appearance, personality, and various traits.

self-righting The inborn drive to remedy a developmental deficit; literally, to return to sitting or standing upright after being tipped over. People of all ages have self-righting impulses, for emotional as well as physical imbalance.

senescence The process of aging, whereby the body becomes less strong and efficient.

sensation The response of a sensory system (eyes, ears, skin, tongue, nose) when it detects a stimulus.

sensitive period A time when a certain type of development is most likely to happen or happens most easily, although it may still happen later with more difficulty. For example, early childhood is considered a sensitive period for language learning.

sensorimotor intelligence Piaget’s term for the way infants think—by using their senses and motor skills—during the first period of cognitive development.

sensory memory The component of the information-processing system in which incoming stimulus information is stored for a split second to allow it to be processed. (Also called the sensory register.)

separation anxiety An infant’s distress when a familiar caregiver leaves; most obvious between 9 and 14 months.

seriation The concept that things can be arranged in a logical series, such as the number sequence or the alphabet.

set point A particular body weight that an individual’s homeostatic processes strive to maintain.

sex differences Biological differences between males and females, in organs, hormones, and body type.

sexual orientation A term that refers to whether a person is sexually and romantically attracted to others of the same sex, the opposite sex, or both sexes.

sexually transmitted infection (STI) A disease spread by sexual contact, including syphilis, gonorrhea, genital herpes, chlamydia, and HIV.

shaken baby syndrome A life-threatening injury that occurs when an infant is forcefully shaken back and forth, a motion that ruptures blood vessels in the brain and breaks neural connections.

single-parent family A family that consists of only one parent and his or her biological children under age 18.

situational couple violence Fighting between romantic partners that is brought on more by the situation than by the deep personality problems of the individuals. Both partners are typically victims and abusers.

slippery slope The argument that a given action will start a chain of events that will culminate in an undesirable outcome.

small for gestational age (SGA) A term for a baby whose birthweight is significantly lower than expected, given the time since conception. For example, a 5-pound (2,265-gram) newborn is considered SGA if born on time but not SGA if born two months early. (Also called small-for-date.)

social clock A timetable based on social norms for accomplishing certain life events such as when to finish school, marry, start a career, have children, and retire.

social comparison The tendency to assess one’s abilities, achievements, social status, and other attributes by measuring them against other people, especially one’s peers.

social construction An idea that is based on shared perceptions, not on objective reality. Many age-related terms, such as childhood, adolescence, yuppie, and senior citizen, are social constructions.

social convoy Collectively, the family members, friends, acquaintances, and even strangers who move through life with an individual.

social learning The acquisition of behavior patterns by observing the behavior of others.

social learning theory An extension of behaviorism that emphasizes the influence that other people have over a person’s behavior. Even without specific reinforcement, every individual learns many things through observation and imitation of other people.

social norms approach A method of reducing risky behavior that uses emerging adults’ desire to follow social norms by making them aware, through the use of surveys, of the prevalence of various behaviors within their peer group.

social referencing Seeking information about how to react to an unfamiliar or ambiguous object or event by observing someone else’s expressions and reactions. That other person becomes a social reference.

social smile A smile evoked by a human face, normally first evident in infants about 6 weeks after birth.

sociocultural theory A newer theory that holds that development results from the dynamic interaction of each person with the surrounding social and cultural forces.

sociodramatic play Pretend play in which children act out various roles and themes in stories that they create.

socioeconomic status (SES) A person’s position in society as determined by income, wealth, occupation, education, and place of residence. (Sometimes called social class.)

socioemotional selectivity theory The theory that older people prioritize regulation of their own emotions and seek familiar social contacts who reinforce generativity, pride, and joy.

specific learning disorder (learning disability) A marked deficit in a particular area of learning that is not caused by an apparent physical disability, by an intellectual disability, or by an unusually stressful home environment.

spermarche A boy’s first ejaculation of sperm. Erections can occur as early as infancy, but ejaculation signals sperm production. Spermarche may occur during sleep (in a “wet dream”) or via direct stimulation.

static reasoning A characteristic of preoperational thought in which a young child thinks that nothing changes. Whatever is now has always been and always will be.

stem cells Cells from which any other specialized type of cell can form.

stereotype threat The possibility that one’s appearance or behavior will be misread to confirm another person’s oversimplified, prejudiced attitudes.

still-face technique An experimental practice in which an adult keeps his or her face unmoving and expressionless in face-to-face interaction with an infant.

strange situation A laboratory procedure for measuring attachment by evoking infants’ reactions to the stress of various adults’ comings and goings in an unfamiliar playroom.

stranger wariness An infant’s expression of concern—a quiet stare while clinging to a familiar person, or a look of fear—when a stranger appears.

stratification theories Theories that emphasize that social forces, particularly those related to a person’s social stratum or social category, limit individual choices and affect a person’s ability to function in late adulthood because past stratification continues to limit life in various ways.

stressor Any situation, event, experience, or other stimulus that causes a person to feel stressed. Many circumstances that seem to be stresses become stressors for some people but not for others.

stunting The failure of children to grow to a normal height for their age due to severe and chronic malnutrition.

subjective thought Thinking that is strongly influenced by personal qualities of the individual thinker, such as past experiences, cultural assumptions, and goals for the future.

substantiated maltreatment Harm or endangerment that has been reported, investigated, and verified.

sudden infant death syndrome (SIDS) A situation in which a seemingly healthy infant, usually between 2 and 6 months old, suddenly stops breathing and dies unexpectedly while asleep.

suicidal ideation Thinking about suicide, usually with some serious emotional and intellectual or cognitive overtones.

sunk cost fallacy The mistaken belief that if money, time, or effort that cannot be recovered (a “sunk cost,” in economic terms) has already been invested in some endeavor, then more should be invested in an effort to reach the goal. Because of this fallacy, people spend money trying to fix a “lemon” of a car or send more troops to fight a losing battle.

superego In psychoanalytic theory, the judgmental part of the personality that internalizes the moral standards of the parents.

survey A research method in which information is collected from a large number of people by interviews, written questionnaires, or some other means.

symbolic thought A major accomplishment of preoperational intelligence that allows a child to think symbolically, including understanding that words can refer to things not seen and that an item, such as a flag, can symbolize something else (in this case, for instance, a country).

synapse The intersection between the axon of one neuron and the dendrites of other neurons.

synaptic gap The pathway across which neurotransmitters carry information from the axon of the sending neuron to the dendrites of the receiving neuron.

synchrony A coordinated, rapid, and smooth exchange of responses between a caregiver and an infant.

synthesis A new idea that integrates the thesis and its antithesis, thus representing a new and more comprehensive level of truth; the third stage of the process of dialectical thinking.