The easy, difficult, and slow-to-warm-up temperament types are three historical patterns of early behavioral style identified by Alexander Thomas and Stella Chess through the New York Longitudinal Study. They describe common configurations of activity, emotional response, biological regularity, and adjustment to novelty. The categories summarize observable tendencies, while the original model's nine temperament dimensions preserve much more individual detail. The best scientific interpretation treats these types as descriptive profiles embedded in development and context, rather than as fixed identities, diagnostic labels, or rules about a child's future. Thomas and Chess, 1977; Rothbart, 2007.
Thomas and Chess changed developmental psychology by placing behavioral individuality at the center of explanations of child development. An infant's usual pace of adaptation, emotional intensity, and response to unfamiliar people or situations could matter for daily experience even when those patterns fell within the normal range. Their approach also made an interactional claim: developmental outcomes depend partly on how caregivers, classrooms, and other environments accommodate a child's way of responding. The phrase goodness of fit names this central relationship. Contemporary research retains this insight while using more refined dimensional measures, multiple informants, longitudinal designs, and culturally diverse samples. Chess and Thomas, 1986; Kiff, Lengua, and Zalewski, 2011.
Origins: The New York Longitudinal Study
The New York Longitudinal Study began in 1956 under the leadership of child psychiatrists Alexander Thomas and Stella Chess, working with colleagues including Herbert Birch, Margaret Hertzig, and Sam Korn. The researchers followed a cohort of 133 children, examining behavioral characteristics from early life onward. Interviews with parents, later reports and observations, and longitudinal clinical inquiry supplied the evidence for the emerging theory. The project was influential because it treated children's distinctive reactions as phenomena worth studying directly, rather than automatically explaining them through parental behavior or symptoms. Its historical sample and procedures also constrain how precisely findings can be transferred to present-day populations. Thomas and Chess, 1977; Thomas and Chess, 1990.
The investigators asked what a child habitually did when routines were interrupted, new people appeared, sensory events became intense, or activities demanded persistence. Their theory described temperament as the style of behavior: how an individual typically approaches an event, responds emotionally, adjusts to change, and regulates engagement. Behavioral style is analytically distinguishable from a person's intellectual ability, values, intentions, or the specific content of a behavior. Two children may learn the same task successfully yet differ greatly in how quickly they approach it or how intensely they react to difficulty. Thomas and Chess, 1977; Hertzig, 2012.
The original research combined detailed dimensions with higher-order descriptive patterns. This two-level arrangement is essential: nine characteristics provide a profile of variation, whereas three named types offer a compact summary of some recurring combinations. The typology did not capture every participating child. Later investigators have used stronger factor-analytic, observational, and person-centered approaches to test which behavioral characteristics cluster together, whether resulting profiles replicate, and how patterns change from infancy to adulthood. Rowe and Plomin, 1977; McDevitt and Lazdauskas, 2026.
The Nine Temperament Dimensions
Activity level
Activity level describes the typical amount and pace of bodily movement. Some infants move vigorously during play, dressing, or transitions; others show a quieter motor style. The dimension concerns a relative pattern observed across suitable occasions and should be interpreted against developmental age, sleep, opportunity to move, and situational constraints. High activity does not automatically mean impulsivity, inattention, or a developmental disorder. The same child's activity can also vary across familiar and unfamiliar environments. In the Thomas and Chess framework, activity level contributed to an overall behavioral profile rather than determining one category by itself. Thomas and Chess, 1977; Rothbart, 2007.
Rhythmicity or regularity
Rhythmicity refers to the predictability of bodily and everyday patterns, such as sleep-wake cycles, hunger, feeding, and elimination. A child whose daily rhythms recur with some regularity may make schedules easier to anticipate, whereas less regular timing can require caregivers to remain flexible. These differences reflect the behavioral organization observed at a given stage; routines, health, developmental transitions, and household schedules can influence their expression. Regularity is not a measure of virtue, compliance, intelligence, or parenting quality. It is one dimension among several, and a single irregular week is not a stable temperament profile. Chess and Thomas, 1986; Thomas and Chess, 1977.
Approach and withdrawal
Initial approach or withdrawal concerns the direction of an early response to unfamiliar people, objects, activities, or circumstances. Approach can look like immediate exploratory interest; withdrawal can take the form of hesitation, looking away, staying close to a familiar caregiver, or initially declining participation. The important qualifier is initial: a first response does not reveal how the child will behave after gaining familiarity. Approach and withdrawal must be studied with attention to the novelty of the stimulus, social expectations, and the child's prior experience. This dimension is especially relevant to understanding slow-to-warm-up behavior without equating it with pathological anxiety. Thomas and Chess, 1977; Rothbart and Bates, 2007.
Adaptability
Adaptability describes the speed and ease with which behavior changes after an initial response to a new or altered situation. It differs from approach-withdrawal because a child can respond cautiously at first yet adapt readily once a setting is understood; another may approach initially and still struggle when a familiar routine changes. Developmental opportunities, caregiver preparation, sensory demands, and repeated experience all shape how adaptation becomes observable. A slower adaptation rate often calls for more time and predictability rather than a judgment that a child is deliberately resistant. Chess and Thomas, 1986; Kiff, Lengua, and Zalewski, 2011.
Threshold of responsiveness
The threshold of responsiveness is the approximate intensity of stimulation needed to produce a noticeable response. A relatively low threshold means a subtle sound, light, texture, or other stimulus may elicit a response, while a higher threshold means more stimulation may be needed. In ordinary language this is often connected with sensitivity, although sensory perception, emotional meaning, and context should be assessed separately. Sensitivity to a noisy room is not equivalent to a psychiatric diagnosis or to an entire personality type. Modern instruments sometimes reorganize these features into somewhat different dimensions, a reminder that theoretical labels and psychometric factors are not necessarily identical. Rowe and Plomin, 1977; Gartstein and Rothbart, 2003.
Intensity of reaction
Intensity concerns the strength of an observable response, whether pleasant or unpleasant. A child may express joy exuberantly, frustration loudly, or surprise dramatically, while another shows more restrained expressions under comparable circumstances. The intensity of an emotion and its emotional direction are different variables: strong delight and strong distress can both reflect high intensity. Caregiver reactions may magnify or calm the social consequences of intense expressions, and developmental changes in language and self-regulation alter how intensity is displayed. The term describes response style rather than a defect in emotional functioning. Thomas and Chess, 1977; Rothbart, 2007.
Quality of mood
Quality of mood addresses the relative prominence of positive and negative emotional expressions in everyday situations. In the original scheme it concerned the child's characteristic emotional tone, not a clinical diagnosis or a measurement of subjective happiness. Observable smiles, irritation, discomfort, and interest can differ in frequency across settings. Mood quality must be distinguished from intensity: frequent mild displeasure and infrequent powerful frustration do not represent the same configuration. Contemporary temperament research often measures negative affectivity and positive emotionality through multiple indicators rather than assuming one overall emotional continuum. Thomas and Chess, 1977; Rothbart and Bates, 2007.
Distractibility
Distractibility refers to the ease with which external events interrupt ongoing behavior. A sound, person, movement, or change in the surroundings may redirect one child's attention more readily than another's. The meaning of this characteristic depends on age, task difficulty, novelty, and the type of interruption. It also differs from a clinical assessment of attention regulation. The original definition should be interpreted alongside modern research distinguishing reactive attention, effortful control, and executive attention, whose developmental courses and measurement procedures differ. Rothbart, 2007; Rothbart and Posner, 2007.
Attention span and persistence
Attention span and persistence concern sustained engagement in an activity and continued effort despite obstacles. A child might return repeatedly to a challenging construction task or move quickly to another activity when frustrated. Opportunity, task appeal, fatigue, motor development, and adult scaffolding can alter observed persistence. These features should not be collapsed into academic ability or personal motivation. Their historical placement among nine broad temperament characteristics remains useful for describing behavioral style, while contemporary developmental models distinguish attentional processes and self-regulatory capacities in greater detail. Thomas and Chess, 1977; Rothbart and Posner, 2007.
The Three Classical Temperament Types
Easy temperament: predictable rhythms and flexible adaptation
The easy profile combined relatively regular biological functions, predominantly positive mood, a generally welcoming response to new experiences, comparatively rapid adaptation, and mild to moderate reaction intensity. In settings that reward predictable schedules and straightforward transitions, these characteristics may reduce the amount of negotiation required in everyday caregiving. The word easy describes how the pattern was experienced in a particular caregiving framework; it does not mean a child has a morally superior personality, always feels happy, or requires less emotional attention. A child with this profile can become distressed, resist a change, or struggle in an unfamiliar context. Chess and Thomas, 1986; Thomas and Chess, 1977.
An illustrative pattern would be an infant whose feeding and rest are fairly predictable, who shows interest in a new toy, and who adjusts to a changed routine after a short interval. Yet the label should not conceal variation among these component characteristics. A child can be regular in sleep but sensitive to noise, or approach strangers readily while showing strong frustration during a difficult task. Interpreting the whole profile requires multiple occasions and more than one observer when possible. The category is most defensible as a broad historical description and less defensible as a precise individualized prediction. Gartstein and Rothbart, 2003; Rothbart and Bates, 2007.
Difficult temperament: intense responses and challenging transitions
The classical difficult profile featured greater irregularity of daily rhythms, frequent negative emotional expressions, withdrawal from unfamiliar stimuli, slower adaptation, and often intense reactions. Parents might encounter more unpredictability in soothing, sleep timing, or transitions and may need to adjust routines more often. The terminology reflects the historical perspective of caregiving demands. It offers no scientific basis for describing a child as bad, oppositional by nature, or destined for emotional or behavioral problems. The same child may respond differently to a supportive environment, and a temperament profile alone does not establish clinical impairment. Thomas and Chess, 1977; Kiff, Lengua, and Zalewski, 2011.
High intensity and negative mood should also be separated analytically. A vigorous reaction to a frustrating delay is not the same as chronic sadness, and irregular feeding or sleeping can have many developmental and environmental explanations. Modern developmental psychopathology investigates specific features such as frustration, fear, impulsivity, and self-regulation because their associations with later difficulties differ according to the child and the caregiving context. The label difficult compresses several potentially independent dimensions into one name. Its usefulness lies in prompting careful investigation of the individual pattern rather than replacing that investigation. Kiff, Lengua, and Zalewski, 2011; Rothbart, 2007.
Slow-to-warm-up temperament: initial caution and gradual engagement
The slow-to-warm-up profile was characterized by an initially hesitant or withdrawing response to novelty, relatively low activity in unfamiliar circumstances, mild or moderate negative reactions, and gradual adaptation as experience accumulated. Unlike the difficult profile, reactions were typically less intense and bodily rhythms were less irregular. What gives this pattern its distinctive meaning is its time course: a child who initially stands back may later engage comfortably after repeated exposure and opportunities to observe. A single quiet encounter therefore provides weak evidence about the child's sociability or capacity for engagement. Thomas and Chess, 1977; Chess and Thomas, 1986.
Imagine a preschooler who stays near a familiar adult when a new group activity begins, watches the other children closely, and joins in after several visits. This course may be entirely consistent with normal temperament variation. It should not be interpreted as proof of social anxiety disorder, selective mutism, an attachment problem, or low self-esteem. Research on behavioral inhibition and later anxiety can help identify prospective associations in specific populations, but childhood caution and later disorder are different constructs with different assessment standards. A meaningful account considers distress, duration, functioning, setting, and developmental stage. Rothbart and Bates, 2007; Kiff, Lengua, and Zalewski, 2011.
Where the Familiar 40, 10, and 15 Percent Figures Came From
Historical summaries of the NYLS report approximately 40% of the original children as easy, 10% as difficult, and 15% as slow to warm up. The remaining approximately 35% did not fit neatly into any one of these three configurations. These figures describe the classification patterns reported for the original study; they are not established prevalence rates for all infants, all countries, or current birth cohorts. Treating the three values as universal percentages would erase both the study's sampling limitations and the sizable residual category. The more scientifically relevant message is that the researchers observed recognizable patterns while also documenting substantial heterogeneity. Thomas and Chess, 1977; McDevitt and Lazdauskas, 2026.
These historical proportions also should not be converted directly into individual probabilities. A parent whose child displays initial withdrawal cannot infer a 15% chance of belonging to a fixed biological kind. Classification rules depend on the instrument, sample, age, and analytical strategy. Current person-centered analyses may yield a different number of profiles and different rates because they pose a different statistical question. Researchers must evaluate class separation, stability, replication, and external validity rather than accepting the original frequencies as a population constant. Rowe and Plomin, 1977; McDevitt and Lazdauskas, 2026.
Goodness of Fit: The Central Developmental Principle
Thomas and Chess used goodness of fit to describe the correspondence between a person's temperament and the demands, expectations, and opportunities of the environment. A cautious child can thrive where new experiences are introduced gradually and familiar support is available; a highly active child may function better where movement is permitted and activities are adapted appropriately. A poor fit arises when settings continually demand responses that are especially difficult for a child's behavioral style, without reasonable accommodation or learning opportunities. This concept locates adaptation in an ongoing child-environment relationship, not in a permanent temperament score. Chess and Thomas, 1986; Chess and Thomas, 1999.
Goodness of fit does not mean adults must remove every frustration or allow every preference to dictate the environment. Children develop skills through safe experiences, clear expectations, shared routines, and opportunities to practice regulation. A fit-oriented approach adjusts the rate, intensity, and support surrounding demands, while retaining developmentally reasonable goals. For example, preparing a child for a transition can make participation more manageable without avoiding the transition indefinitely. The concept is a framework for interpreting reciprocal adjustment and requires evidence before any particular parenting technique can be called effective. Kiff, Lengua, and Zalewski, 2011; Rothbart and Posner, 2007.
Contemporary research strengthens the interactional account by studying how parenting influences child characteristics and how child characteristics evoke responses from adults. The systematic review by Kiff, Lengua, and Zalewski examined bidirectional and interactive pathways involving frustration, fear, impulsivity, and self-regulation. Its findings support the view that the effects of parenting can depend on a child's characteristics and that child behavior can also contribute to changes in parenting behavior. These are probabilistic processes embedded in families, wider social resources, and developmental time. They do not imply that a parent caused the child's temperament or that every outcome can be explained by one caregiver-child interaction. Kiff, Lengua, and Zalewski, 2011.
Temperament, Personality Traits, and Momentary States
Temperament refers to relatively early-emerging individual differences in emotional, motivational, attentional, and behavioral reactivity and regulation. Personality is a broader description of characteristic psychological patterns that can include goals, values, beliefs, self-concept, and enduring traits shaped over development. A temperament pattern can contribute to later personality without fully determining it. A momentary state is a response occurring in a particular situation, such as one episode of hesitation or excitement. Observing that state is one data point, not proof that the child belongs to a temperament type. Rothbart, 2007; Rothbart and Bates, 2007.
The original model's emphasis on behavioral style remains compatible with this distinction. A characteristic threshold of response can influence how often a child reacts to a sound, but an unexpected loud event can provoke nearly anyone. A child who usually approaches novelty may hesitate after an upsetting experience. Consequently, inference about temperament requires repeated observations that separate typical tendencies from unusual circumstances. Developmental research further shows that the behavioral manifestation of a disposition may change with age, language, new responsibilities, and regulatory skills. Putnam, Rothbart, and Gartstein, 2008; Rothbart and Posner, 2007.
Stability, Change, and Developmental Trajectories
Temperament is often described as relatively stable, but stability has several meanings. Rank-order stability concerns whether children maintain their relative positions compared with their peers. Mean-level change concerns whether the group becomes more or less reactive, attentive, or regulated over time. These two patterns can coexist. A child may remain more cautious than peers while becoming considerably more comfortable in social settings as language, experience, and regulation develop. The content of age-appropriate measures must also change when behavior available to an infant differs from behavior available to a school-age child. Putnam, Rothbart, and Gartstein, 2008; Rothbart, 2007.
Longitudinal studies provide evidence for continuity in some temperament dimensions, alongside meaningful change and context dependence. They are more informative than a single parental questionnaire because they can examine trajectories, transitions, and subsequent outcomes. Yet prediction at the group level is not destiny for an individual child. Even when an early measure correlates with a later trait, overlapping distributions and unmeasured influences limit the precision of any personal forecast. Biological maturation, relationships, new learning, stress, and opportunities for regulation all contribute to the evolving expression of temperament. Putnam, Rothbart, and Gartstein, 2008; Kiff, Lengua, and Zalewski, 2011.
Long-term personality research also shows that early behavioral styles can be associated with adult traits, while the form and meaning of the behavior change across the lifespan. Such associations make temperament scientifically relevant to personality development, but they do not validate a literal childhood-to-adulthood mapping of the three original labels. It remains useful to study the constituent dimensions, developmental pathways, and changing contexts rather than assuming that children permanently remain easy, difficult, or slow to warm up. Caspi and Silva, 1995; Rothbart, 2007.
How Contemporary Research Measures Temperament
The New York Longitudinal Study relied heavily on detailed caregiver interviews and longitudinal clinical interpretation. Contemporary investigations also use age-specific questionnaires, direct observation, structured laboratory episodes, educator reports, and, where appropriate, physiological measures. The Revised Infant Behavior Questionnaire, for example, assesses numerous fine-grained infant characteristics rather than asking parents simply to assign one of three types. Agreement between informants and methods matters because caregivers encounter different situations and may interpret responses differently. Gartstein and Rothbart, 2003; Rothbart and Bates, 2007.
Parent reports provide valuable access to behavior repeated across ordinary days, but they can be influenced by expectations, stress, comparison groups, and the circumstances in which the child is observed. Laboratory observation offers greater control over stimuli, yet a brief unfamiliar setting may exaggerate novelty responses. A teacher may see persistence or sociability that a parent has fewer opportunities to observe. Scientific interpretation improves when investigators define the construct clearly and assess converging evidence without assuming that any one method is a transparent window into an immutable temperament. Gartstein and Rothbart, 2003; Rowe and Plomin, 1977.
Statistical profiles introduce an additional methodological choice. Dimensional scores preserve relative variation on each characteristic; latent-profile models seek groups with similar multivariate patterns. A latent profile is a statistical summary conditional on selected indicators and modeling assumptions. It is not automatically a natural biological category. Independent replication, age-specific validation, and assessment of predictive usefulness determine whether a profile adds knowledge beyond its component dimensions. This distinction is central to modern reassessments of the easy, difficult, and slow-to-warm-up framework. McDevitt and Lazdauskas, 2026; Rowe and Plomin, 1977.
What New Research Says About the Three-Type Model
Contemporary temperament theory frequently organizes child behavior around broad processes such as surgency or positive approach, negative affectivity, and effortful control. These dimensions are not exact renamings of the original nine NYLS categories, but they cover related aspects of activity, emotional response, and developing regulation. Rothbart's account pays particular attention to how attentional regulation emerges and interacts with reactive tendencies. The conceptual change is significant: a child can show substantial reactivity alongside substantial self-regulatory capacity, and the two should be measured distinctly. Rothbart, 2007; Rothbart and Posner, 2007.
An empirical reassessment published in 2026 by McDevitt and Lazdauskas used latent-profile analysis of adult self-reported temperament in 1,260 respondents from the United States and Lithuania. Its preferred five-profile solution included patterns resembling the classical easy, difficult, and slow-to-warm-up types, together with additional profiles labeled curious and shy. This is relevant evidence that three types may not exhaust the range of possible configurations. Its interpretation is preliminary for childhood temperament: the study assessed adults, used self-report and nonprobability recruitment, and did not establish five universal types among infants. Replication in different populations and developmental periods is needed before attaching a general prevalence claim to the new profiles. McDevitt and Lazdauskas, 2026.
The best-supported conclusion is therefore more specific than either complete acceptance or rejection of the classic typology. The New York Longitudinal Study documented informative patterns and advanced interactional developmental theory. Later research has strengthened measurement and revealed alternative factor and profile structures. Whether a particular classification is useful depends on its purpose: communicating a broad style, testing developmental hypotheses, or making an individual prediction require different degrees of precision and validation. The original terms can serve historical and educational explanation, provided the nine dimensions and limits of the grouping remain visible. Rothbart and Bates, 2007; McDevitt and Lazdauskas, 2026.
Cultural Context and Generalizability
The familiar NYLS proportions originated in a limited historical research setting. Social expectations about independence, expressiveness, routines, obedience, and sociability differ among families and societies, influencing which behaviors are noticed and how adults evaluate them. Some aspects of emotional and attentional variation appear across populations, but this does not make historical type frequencies universal. Cross-cultural comparison must establish that translated items, observer judgments, and measurement structures capture comparable psychological constructs. Gartstein, Slobodskaya, and Kinsht, 2003; Putnam and colleagues, 2024.
The Global Temperament Project analyzed 83,423 parent reports across 341 samples from 59 countries, illustrating the scale and diversity of current cross-cultural temperament research. Its broad measures address surgency, negative affectivity, and regulatory capacity, not a direct replication of the three NYLS type percentages. Thus, even an exceptionally large multinational dataset cannot automatically certify the prevalence of easy, difficult, and slow-to-warm-up children unless those categories were operationalized and tested. Findings about cross-national differences also require attention to sampling, parent-report bias, and cultural measurement equivalence. Putnam and colleagues, 2024.
Biological and Environmental Influences
Current science understands temperament as developing through multiple interacting biological and environmental pathways. Genetic variation, neurodevelopment, arousal systems, experience, and regulatory learning can contribute to observed behavior, while their relative roles vary by characteristic and developmental period. A heritability estimate, when available, describes variation within a specified population and environment; it does not reveal what percentage of one person's temperament was caused by genes or establish a fixed limit on development. The NYLS three-type labels cannot be traced responsibly to a single gene, transmitter, or brain region. Rothbart and Bates, 2007; Rothbart and Posner, 2007.
Environmental experience influences both how dispositions are expressed and how others interpret them. A classroom with predictable transitions may reduce visible distress in a child sensitive to sudden changes. A peer group that welcomes quieter participation may reveal social interest obscured by pressure for immediate performance. These effects do not negate biological contributions; they show why behavioral outcomes require models that include the person's characteristics, the environment, and their transactions over time. Kiff, Lengua, and Zalewski, 2011; Chess and Thomas, 1999.
Normative Variation, Mental Health, and Ethical Interpretation
Temperament categories are descriptive constructs, not mental-disorder diagnoses. High emotional intensity, caution with unfamiliar people, a low sensory threshold, or an irregular sleep pattern may occur in developmentally typical children. Clinical assessment asks further questions about severity, persistence, functional impairment, developmental expectations, physical health, and the child's wider context. A questionnaire or informal classification cannot establish a psychiatric disorder, and diagnostic categories should not be inferred from words such as difficult or slow to warm up. Rothbart, 2007; Kiff, Lengua, and Zalewski, 2011.
Longitudinal associations between characteristics such as fearfulness, irritability, or weak regulation and later difficulties can help scientists identify developmental pathways and moderators. Statistical association is not sufficient to establish a cause, and average differences among groups do not permit confident individual prediction. Clinical care addresses the child's actual symptoms, developmental history, safety, and functioning rather than treating a temperament type as an intervention target. The most ethical everyday use of the framework is to replace moral judgments with careful observation and responsive environmental design. Kiff, Lengua, and Zalewski, 2011; Rothbart and Bates, 2007.
The language itself deserves scrutiny. Calling one pattern easy can imply that other children are somehow less desirable; calling another difficult can turn a caregiver's experience into a child's identity. Researchers and educators can retain the historical terms when explaining Thomas and Chess while describing living children with concrete behavioral characteristics. Saying that a child usually requires preparation for unfamiliar activities is more informative than saying the child is difficult. Language influences expectations, opportunities, and the interpretation of subsequent behavior, which makes precise, nonstigmatizing descriptions a practical scientific responsibility. Chess and Thomas, 1986; Kiff, Lengua, and Zalewski, 2011.
What the Framework Can Contribute to Everyday Understanding
The dimensions provide a structured way to observe daily transitions without assuming that an isolated reaction defines a person. If a child struggles with a new activity, adults can ask whether the problem involves initial withdrawal, slow adaptability, excessive stimulation, interrupted rhythms, or a mismatch between expectations and available support. Each question points to a different potentially modifiable feature of the environment. Observation over time matters because the same behavior can arise from fatigue, unfamiliarity, health concerns, or an enduring tendency, and those possibilities demand different interpretations. Thomas and Chess, 1977; Chess and Thomas, 1986.
For a child who warms up gradually, allowing time to watch before joining a group may create an opportunity for successful engagement. For a child with intense emotional responses, a calm adult response and clear routine may support developing self-regulation. For a child with less regular bodily rhythms, flexibility and careful attention to sleep and feeding contexts may be more useful than moralizing about compliance. Such examples are practical interpretations of goodness of fit rather than treatments proven by the historical typology. Evidence-based decisions should consider the child's needs, family circumstances, and the available research on the specific problem. Kiff, Lengua, and Zalewski, 2011; Rothbart and Posner, 2007.
Frequently Asked Questions
Are the easy, difficult, and slow-to-warm-up types still scientifically accepted?
They remain influential historical descriptions and teaching tools. Current research more often measures continuous temperament dimensions and sometimes uses empirically derived profiles. The three categories do not constitute a universally validated classification of every child. The original nine dimensions and the principle of goodness of fit remain important contributions; later studies refine the structure and test the degree to which profiles generalize. Rothbart and Bates, 2007; McDevitt and Lazdauskas, 2026.
Can a child display characteristics of more than one type?
Yes. A child can have relatively regular sleep, strong emotional reactions, slow adaptation to novelty, and high persistence at the same time. The original study already contained many children whose combinations could not be assigned neatly to one of the three named groups. Dimensional descriptions therefore often communicate an individual's behavioral style more accurately than a single category. Thomas and Chess, 1977; Rowe and Plomin, 1977.
Does a difficult temperament predict a mental disorder?
A historical difficult label is not a diagnosis and does not establish an individual prognosis. Certain measured dimensions, including high negative emotionality or challenges in regulation, may be associated with later difficulties in some longitudinal research. The relationships vary with parenting, context, measurement, and other developmental factors. Evaluation of a clinical condition requires its own evidence and standards. Kiff, Lengua, and Zalewski, 2011; Rothbart, 2007.
Is slow-to-warm-up temperament the same as shyness or behavioral inhibition?
These constructs overlap in initial caution and responses to novelty, but they are not identical measures. The NYLS slow-to-warm-up profile combines several dimensions, including adaptation speed and reaction intensity. Behavioral inhibition studies often use specific patterns of fearful or restrained reactions to novelty, while shyness commonly concerns social discomfort or reticence. Their definitions, methods, and developmental implications must be compared explicitly rather than substituted for one another. Rothbart and Bates, 2007; Rothbart, 2007.
Can parenting change a child's temperament?
Behavioral patterns can change as children mature and learn, and parenting can shape how temperament is expressed, regulated, and responded to. The interaction is often reciprocal: children also influence caregiver behavior. This does not mean parents can choose an infant's initial temperament or guarantee a particular developmental outcome. Matching support to individual needs while building adaptive skills is more faithful to the scientific literature than promising to transform one type into another. Kiff, Lengua, and Zalewski, 2011; Putnam, Rothbart, and Gartstein, 2008.
What is the main limitation of the Thomas and Chess typology?
The three profiles reduce nine varying characteristics to a small number of labels. Their original distribution arose from a limited historical cohort, many children were unclassified, and later research has not established the three groups as universal natural kinds. Their enduring value lies in the empirical attention to behavioral individuality and the interaction between a child's style and a responsive environment. Thomas and Chess, 1990; McDevitt and Lazdauskas, 2026.
Related Articles
Cluster Personality Traits, Temperament and Individual Differences — the central scientific chapter on traits, temperament, mechanisms, development, and individual differences.
What Is Temperament in Psychology? Definition, Models and Development — the conceptual and developmental foundation of temperament science.
Rothbart's Temperament Model: Reactivity and Effortful Control — a contemporary dimensional account of emotional reactivity and self-regulation.
Infant Temperament: Reactivity, Self-Regulation and Early Development — age-sensitive evidence concerning the emergence of early individual differences.
Behavioral Inhibition in Childhood: Meaning, Development and Anxiety Risk — a complementary analysis of inhibited behavior, continuity, and risk interpretation.
References
Caspi, A., and Silva, P. A. (1995). Temperamental qualities at age three predict personality traits in young adulthood: Longitudinal evidence from a birth cohort. Child Development, 66, 486–498. https://doi.org/10.1111/j.1467-8624.1995.tb00885.x
Chess, S., and Thomas, A. (1986). Temperament in Clinical Practice. Guilford Press. Publisher record
Chess, S., and Thomas, A. (1999). Goodness of Fit: Clinical Applications, From Infancy Through Adult Life. Brunner/Mazel. https://doi.org/10.4324/9780203727607
Gartstein, M. A., and Rothbart, M. K. (2003). Studying infant temperament via the Revised Infant Behavior Questionnaire. Infant Behavior and Development, 26, 64–86. https://doi.org/10.1016/S0163-6383(02)00169-8
Gartstein, M. A., Slobodskaya, H. R., and Kinsht, I. A. (2003). Cross-cultural differences in temperament in the first year of life: United States of America and Russia. International Journal of Behavioral Development, 27, 316–328. https://doi.org/10.1080/01650250244000344
Hertzig, M. E. (2012). Temperament: Then and now. Journal of Nervous and Mental Disease, 200, 659–663. https://doi.org/10.1097/NMD.0b013e3182613fd1
Kiff, C. J., Lengua, L. J., and Zalewski, M. (2011). Nature and nurturing: Parenting in the context of child temperament. Clinical Child and Family Psychology Review, 14, 251–301. https://doi.org/10.1007/s10567-011-0093-4
McDevitt, S. C., and Lazdauskas, T. (2026). New York Longitudinal Study temperament types revisited: A latent profile analysis of individual differences in adults. Behavioral Psychology/Psicología Conductual, 34(1), 45740. https://doi.org/10.31083/BP45740
Putnam, S. P., Rothbart, M. K., and Gartstein, M. A. (2008). Homotypic and heterotypic continuity of fine-grained temperament during infancy, toddlerhood, and early childhood. Infant and Child Development. https://doi.org/10.1002/icd.582
Putnam, S. P., Sehic, E., French, B. F., Gartstein, M. A., Lira Luttges, B., and Global Temperament Project collaborators. (2024). The Global Temperament Project: Parent-reported temperament in infants, toddlers, and children from 59 nations. Developmental Psychology, 60, 916–941. https://doi.org/10.1037/dev0001732
Rothbart, M. K. (2007). Temperament, development, and personality. Current Directions in Psychological Science, 16, 207–212. https://doi.org/10.1111/j.1467-8721.2007.00505.x
Rothbart, M. K., and Bates, J. E. (2007). Temperament. In Handbook of Child Psychology. Wiley. https://doi.org/10.1002/9780470147658.chpsy0303
Rothbart, M. K., and Posner, M. I. (2007). Executive attention and effortful control: Linking temperament, brain networks, and genes. Child Development Perspectives, 1. https://doi.org/10.1111/j.1750-8606.2007.00002.x
Rowe, D. C., and Plomin, R. (1977). Temperament in early childhood. Journal of Personality Assessment, 41, 150–156. https://doi.org/10.1207/s15327752jpa4102_5
Thomas, A., and Chess, S. (1977). Temperament and Development. Brunner/Mazel. Publisher bibliographic record
Thomas, A., and Chess, S. (1990). Studies in temperament: A paradigm in psychosocial research. PubMed record