3.2 Models of child development
All approaches to child development emphasise that there are particularly sensitive periods before birth, in childhood and in adolescence when optimal developmental changes occur, but that change is not confined to these periods. Children who “miss out” at important times can “catch up”, but this becomes progressively more difficult to accomplish with age. Failure to provide a supportive environment for child development can generate very large costs in later life for government and society as a whole. All approaches emphasise that development over time is influenced, but not wholly determined, by what has gone before. The outcomes of development at one life-stage are likely to lead to similar outcomes at later stages in the absence of specific interventions to alter trajectories.
These insights underline the importance of trying to give children a good start in life, particularly those who are statistically “at-risk” of poor outcomes. However, early life cannot be an exclusive focus for policy since not all people who do badly in adulthood exhibit risk factors at earlier stages and not all who do well enjoy favourable circumstances in childhood.
There is no single, relatively simple, robust account of the main determinants of adult outcomes. Much of the variation in outcomes remains unexplained. There are a number of approaches to understanding the potential range of factors implicated in child and later adult well-being. They attempt, first, to document the universal principles underlying the development of all children and, secondly, to explain individual differences between children, why good outcomes and bad outcomes tend to coincide in the same people and why some children appear to do well despite the odds.
The most widely accepted, transactional, theory of child development focuses on the interplay between the characteristics of the individual child and the influences of its environment to explain physical, social and cognitive development (Chase-Lansdale 1998). For example, the stress of socio-economic problems such as poverty may limit the ability of many parents to act as effectively as they might. However, the precise causal links, as opposed to correlations, between poverty and children’s outcomes are likely to be complex since unmeasured variables leading both to poverty and children’s outcomes cannot be ruled out (Mayer 1997).
Transactional theory has been increasingly influenced in recent years by behavioural genetics, neuropsychology and psychophysiology because of increasing evidence of the importance of genetic influences and biological factors in child development. The interaction between genetic characteristics and environmental experiences may help explain why some children do well despite a seemingly negative upbringing and vice versa.
Developmental theory supports three general principles of child development (Chase-Lansdale 1998). First, the past is a good predictor of the future, since large changes are limited by what has gone before, although change is possible at every point in development up to and into adulthood. Secondly, there are especially sensitive periods in the developmental trajectory when certain changes occur. This does not mean that change is impossible later, but that it is not as easy as putting in place a secure base in early childhood. Finally, change can occur throughout life, but there is more evidence for malleability in the early years than in later periods.
There is considerable variation in outcomes among individuals. There are also consistent cross-sectional associations between the socio-economic status of individuals and a wide range of developmental outcomes such as physical and mental health, behavioural adjustment, coping skills and educational attainment (Keating and Hertzman 1999).
There are a number of ways that outcomes can be affected. Latent effects are those causal factors that have a lifelong impact on well-being, independent of intervening experience (although the intervening experiences may have the effect of magnifying or diminishing the impact of latent effects). Pathway effects are those causal factors that shape subsequent life trajectories. A third set of influences is cumulative. The effect on outcomes is due to the accumulation of advantage or disadvantage over time based on the duration and intensity of exposure to a range of risk and protective factors. In practice, it can be difficult to disentangle the latent, pathway and cumulative effects shaping adult outcomes.
The notion of latent effects reflects the findings of developmental psychology that there are particularly sensitive periods before birth, in childhood and in adolescence when optimal developmental changes occur, but that change is not confined to these periods (Zuckerman and Kahn 2000). Opportunities to develop particular competencies occur at unique times in early life, and are socially patterned. Developing these competencies has life-long effects on well-being, regardless of intervening experience.
Brain science suggests that brains are changed by early experiences in ways that are difficult to reverse later (McCain and Mustard 1999). Experiences of nurture, stimulation, and support, and opportunities for exploration of the immediate environment, shape the brain positively and enduringly in early life. However, the use of modern brain science to draw conclusions about critical periods in human development with crucial implications for later outcomes remains debated (Bruer 1998, Mustard 2000). Adding weight to latency theory is research linking foetal and infant conditions, such as malnutrition, with adult physical health (Barker 1992, Marmot and Wadsworth 1997).
Although some adverse experiences are biologically encoded such that they are virtually irreversible, there is sufficient evidence of flexibility to indicate that not all biological embedding is deterministic. For example, not all children who experience nutritional deficits in utero have poor outcomes in later life. However, the evidence suggests that the negative effects of adverse experiences in early childhood are harder to overcome later in development, underlining the importance of giving children a good start in life.
Under the pathways model, risks of poor outcomes accumulate over time, rather than being significant from the outset as in the latency model. Such a pathway may begin with infant stress leading to lack of school readiness, leading to behavioural problems at school, leading to school failure, leading to poor mental health in adulthood. While the effect is cumulative, intervention at any time can influence the life course, albeit less effectively in later life because of the limiting effects of previous latent factors.
It is important for policy development and intervention design to have some idea of whether latent and pathway effects on development are complementary or mutually exclusive. If both sets of factors are important, one may be more important than the other in influencing adult outcomes and at which points in the life cycle. However, even with longitudinal data it is difficult to distinguish latent and pathway effects. Overall, the insights from the latent and pathways models indicate that intervention and prevention strategies aimed at improving childhood and subsequent adult outcomes stand a greater chance of success if they are aimed at core developmental processes (eg, language acquisition) and occur at important transition points in children’s development (eg, diverting children from problematic pathways by intervening before entry to school). It is also important to improve early experience since this conditions neurophysiological development which has long term effects (Keating and Hertzman 1999).
