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A lot of parents have, at some point, thought: "My child is difficult to raise." Won't stop crying. Can't adapt to new places. Mood swings are unpredictable. Nothing seems to work.
These experiences are more likely to reflect the child's inborn temperament than any failure of parenting. The trouble is that "hard to raise" tends to slide toward "there is a hard-to-raise child" — a fixed attribute attached to the child. What temperament research has consistently found instead is that "hard to raise" is not a static property of the child but a dynamic phenomenon arising from the combination of child and environment.
The New York Longitudinal Study
In 1956, child psychiatrists Alexander Thomas and Stella Chess began a longitudinal study of 133 infants in New York City. This became the New York Longitudinal Study (NYLS) [1].
Most developmental research at the time explained children's outcomes primarily through maternal behavior. Thomas and Chess questioned that assumption. Even children from the same household, raised by the same parents, are different from the start. The stable individual differences in that "differentness" are what they called temperament: biologically based, stable individual differences in behavioral style, emotional reactivity, and self-regulation present from early infancy.
The research team identified nine temperament dimensions — activity level, rhythmicity (regularity of biological cycles), approach or withdrawal in response to novelty, adaptability, threshold of responsiveness, intensity of reaction, quality of mood, distractibility, and attention span and persistence — and used those profiles to classify children into three broad types [1]:
- Easy (~40%): Regular rhythms, positive responses to new stimuli, generally pleasant mood.
- Difficult (~10%): Irregular rhythms, withdrawal from novelty, intense reactions, predominantly negative mood.
- Slow-to-warm-up (~15%): Low activity level, initial withdrawal from novelty but gradual adaptation, low intensity.
The remaining roughly 35% did not fit clearly into any of these types and were classified as mixed.
Temperament Is Not Fate
One of the most important findings Thomas and Chess emphasized is that children with "difficult" temperament do not invariably develop behavioral problems [1]. What determined whether behavioral problems emerged was not temperament itself but the goodness of fit: the degree of match between a child's temperamental characteristics and the demands, expectations, and opportunities of their environment between temperament and environment — above all, between the child's temperament and the caregiver.
The "goodness of fit" model is the core of their theory. When a child's temperamental characteristics align with the demands, expectations, and opportunities of the environment, development is facilitated. When they do not — when fit is poor — the same temperament becomes more likely to produce behavioral difficulties [1].
Consider a child with low adaptability and a tendency to withdraw from novelty. Brought to a new setting every week, or moved frequently, that child will show high stress. Give the same child a stable environment with adequate time to adjust, and she will gradually adapt. The difficulty is not a fixed attribute; it emerges from the combination of child and circumstance.
Kagan's Behavioral Inhibition Research
Jerome Kagan at Harvard extended the Thomas and Chess framework with longitudinal research focused specifically on behavioral inhibition [2].
Kagan and colleagues observed that roughly 20% of four-month-old infants show high motor activity and distress in response to novel stimuli — a pattern they labeled "high-reactive." These high-reactive infants were more likely to show behavioral inhibition: a temperament pattern of caution, shyness, and withdrawal in novel situations, linked to higher physiological reactivity in toddlerhood: extreme caution, shyness, and withdrawal in the face of new people, places, and situations [2,5].
Importantly, not all high-reactive infants became highly inhibited toddlers. The caregiving environment — specifically, how parents responded — moderated subsequent expression. Attempting to forcibly correct "shyness" or "cautiousness" tends to heighten the child's stress and can worsen the very outcomes the parent is trying to change. Understanding the child's pace and allowing repeated, graduated exposure to novel situations is what supports adaptation over time.
Rothbart's Three-Dimension Model
Mary Rothbart extended temperament research further, proposing a model built around three dimensions: extraversion/surgency, negative emotionality, and effortful control: the capacity to deliberately shift attention, inhibit a dominant response, and plan behavior; strongly predicts later self-regulation and academic adjustment [3].
Effortful control — the capacity to shift attention, inhibit impulses, and plan behavior — develops from infancy onward and is strongly associated with later self-regulation, academic adjustment, and social competence [3]. In observable behavior, it appears as the ability to wait, or as relative resistance to distraction.
Rothbart's model integrates and reorganizes the nine Thomas-and-Chess dimensions and is now widely used in research, connecting directly to work on the neurobiological underpinnings of temperament [3].
What Parents Can Do
Temperament, at least in the early years, is not easily changed. But it can be understood.
The first step is observing the child's temperamental profile. "How long does it take before she's comfortable in a new setting?" "What level of stimulation hits her limit?" "How long before her mood recovers?" These are patterns that emerge through daily records. Keeping a log over months does not just document milestones; it reveals a child's characteristic rhythms.
The second step is reframing "hard to raise" — moving it from a fixed label attached to the child toward "a challenge arising from this particular child in this particular environment right now." The practical implication of the goodness-of-fit model is that, before trying to change the child, it is worth asking whether the environment can be adjusted [1].
The third step is being cautious about simplistic categorization. The three NYLS types are a rough sketch of the profile landscape, and 35% of children don't fit neatly into any of them. Labels can help understanding; they can also obscure the actual complexity of the child in front of you.
Continuous parenting records make visible something like: "Last month, every new place meant tears. This month, five minutes and she's fine." The stable core of a child's temperament persists, but the range of adaptation expands with development. Seeing that change along the vertical axis of records — rather than comparing sideways to other children — is its own evidence against the fear "will she be like this forever?"
Summary
"Hard to raise" is not a parenting failure and not a flaw in the child. What Thomas and Chess began documenting more than half a century ago is that temperament — stable individual differences that appear from birth — exists, and that how well a child's temperament fits her environment shapes how she develops [1].
Temperament cannot be changed, but it can be understood. And understanding it makes it possible to adjust the environment more thoughtfully. When "this is the kind of child she is" becomes the starting point for observation rather than a source of frustration, parenting acquires a few more handholds.
References
- Thomas A, Chess S. Temperament and Development. New York: Brunner/Mazel; 1977.
- Kagan J. Galen's Prophecy: Temperament in Human Nature. New York: Basic Books; 1994.
- Rothbart MK. Temperament, development, and personality. Curr Dir Psychol Sci. 2007;16(4):207–212. doi:10.1111/j.1467-8721.2007.00505.x.
- Chess S, Thomas A. Temperament and its functional significance. In: Greenspan SI, Pollock GH, eds. The Course of Life, Vol. 2. Madison, CT: International Universities Press; 1989:163–228. [unverified: book chapter; no DOI or PMID; the Japanese editorial note recommends replacement with a primary journal article if available]
- Kagan J, Snidman N, Arcus D. Childhood derivatives of high and low reactivity in infancy. Child Dev. 1998;69(6):1483–1493. doi:10.1111/j.1467-8624.1998.tb06171.x. PMID: 9914634.
- Rothbart MK, Bates JE. Temperament. In: Damon W, Lerner R, Eisenberg N, eds. Handbook of Child Psychology, Vol. 3: Social, Emotional, and Personality Development. 6th ed. Hoboken, NJ: Wiley; 2006:99–166. [unverified: book chapter; no DOI or PMID; the Japanese editorial note suggests this may be redundant given [3] and recommends removing or consolidating]