Critical periods in childhood learning

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learning has lasting effects on development although they are rarely irreversible. Nature and nurture: .... Piaget's stages of mental development in young children.
Critical periods in childhood learning Kathy Sylva Department of Child Development and Primary Education, Institute of Education, London, UK

The human baby is bom with 'hard wiring' that loads the baby to pay attention to certain things in the environment, especially the communications of canegivers. These inborn predispositions are gradually shaped by the environment of the family, a 'curriculum for babies' which isrichon communication and making sense of the world. Day care and nursery education can complement and enhance the child's learning, especially if they are of high quality. Research has shown again and again that early learning has lasting effects on development although they are rarely irreversible.

Nature and nurture: an ancient but current debate This is one of the oldest and most central debates in science. When discussed by a psychologist it concerns whether a child's development is governed by a pattern built in at birth or whether it is moulded by experiences afterwards. Historically the nativist side to the debate, the side which championed nature, was represented by Plato who believed that many concepts were innate. On the other side, British 'empiricists' such as John Locke insisted that the baby's mind is a blank slate at birth and that all knowledge is etched on it by experience. There is now widespread agreement that the 'interactionists' have won the day and that child development is governed by the interaction of nature and nurture. Still there is heated debate about how much of a child's genes contribute to the child's eventual intellectual attainment and personal style. This paper leaves the topic of genes to other authors in the volume while concentrating on what is known about learning in young children, especially the power of the environment to shape it.

Inborn bias and constraints pTic/nth!™ Department of C/11W Deve/opmentond PnmaryEducation, Institute or Education,

20 Bedford Way, LondonWOHOAL, UK

contemporary version of the naturist view focuses on 'inborn biases'. These constraints on development do not consist of Plato's inborn concepts but rather ways the newborn is 'programmed' to pay m o r e attention to some things than to others and to respond in a . .

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particular way to certain objects. For example, Slobin1 proposes that babies are born with what he calls 'operating principles' that

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determine which aspects of the auditory environment they selectively attend to and the systematic ways they try to make sense of speech sounds. Aspects of the speech environment which babies pay special attention to are the beginnings and ends to the human speech stream. It's similar in visual perception; psychologists such as Haith2 claim that babies have an inborn predisposition to pay special attention to movement and to shifts between dark and light. Although such biases in perception are inborn starting points for learning, new skills and knowledge will be influenced profoundly by experience. However, these biases constrain the developmental pathways that are possible3; theories of complete plasticity in human nature have not withstood scientific test. 186

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How nurture modulates nature Understanding of the interaction between nature and nurture has become more subtle and powerful. Richard Aslin4 proposes five models to describe the potential impact on children's development of the childhood environment in which they grow up (see Fig. 1). The first model assumes absolutely no environmental effect on the developing skill: the second assumes that certain environmental support is necessary for the maintenance of a skill or behaviour but that its form is innate. In the third model the environment facilitates the earlier or later appearance of a skill or behaviour which is programmed by the genes. The last two models show a considerable impact of the environment. In the fourth model, the environment's shaping leads to lasting higher or lower performance. For example, it is known that parents who talk to their children have offspring with higher IQs5. Finally the fifth model describes skills or behaviours which are shaped completely by the child's experiences. Exposing a child to a second language is a good example of the fifth model because the environment determines all.

The timing of experience: or 'critical periods' The impact of nurture can vary according to its timing. For example, the impact of day care on a child may differ according to its occurrence in the first year of a child's life or the years right before school6. The best known example of a critical period in animal development is that young ducks will become imprinted on any moving object in their immediate environment at approximately 15 h after hatching. If they do not experience a moving object during this critical period they will fail to become imprinted at all7. The broader concept of a sensitive period in human development has supplanted the notion of critical periods. A sensitive period may last for months or even years and denotes the time in which the developing child is particularly responsive to certain forms of experience or particularly hindered by their absence. A good example is the fact that children in the period 6-18 months are particularly sensitive to caretaking and that this is the time when they must develop their core attachment to their parents8. Other periods may be particularly important for intellectual or linguistic development, for example the period 12-30 months when language develops so rapidly9. Bnfah Mtdical Bulletm 1997,53 (No. 1)

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The ecology of development Until recently, most research on child development concentrated on the child's immediate environment, which was the family throughout infancy, followed by the school and the peer group. Bronfrenbrenner10 deplores this tunnel vision and argues forcefully that the child's immediate environment is influenced by broad social factors, such as cultural beliefs or the distribution of health care. Moreover, even the environment of the family is not unidimensional; each child inhabits a unique space which is defined by siblings, the age of their parents when they were born and a host of other 'ecological factors' which may be unique to them or their family. (Imagine the difference between the experiences of the first child born to a Pakistani family who later moved to Britain and her much younger sibling born 15 years later in a large city. It would be impossible to imagine that the 'family' influences on these two children were not vastly different.) An understanding of early learning and its environment will have to include the social institutions related to childcare as well as the family.

The 'pre-adapted' newborn To understand how very young babies learn, we must return to nature and nurture. Babies' perception of complex patterning provides a good example of how the infant's 'wiring' influences what it learns about the visual world. Newborns and infants have far more sensory capacity than doctors or psychologists have suspected. Babies' motor skills are limited for many months and perhaps professionals assumed that sensory skills were as well. Although the newborn baby does not have the sensory capacities of a 6 month old, most of the basic perceptual skills are functioning at some level immediately after birth. The newborn is much better at getting information about the world than at acting on it. Although newborns cannot judge depth at birth and are clumsy at reaching, their behaviour is governed immediately by visual information which they process quite efficiently. Babies look at the world in a systematic way. Haith2 says 'there are rules babies look by' and adds that the rules change with age. At first, visual attention is focused on where objects are but a change takes place around 2 months such that attention is drawn more to the characteristics of objects rather than their location11. The baby moves from a visual strategy for 'finding where things are' to one of 'finding out about things'. It's not known whether this shift is affected by learning but it is certainly an inborn disposition, 18 8

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since babies reared in vastly different environments all go through the same perceptual shift. Most interesting of all, learning concerns the baby's recognition of the parents. Walton et at11, showed newborns videos of their own mothers contrasted with videos of a woman with similar hair colour, eyes, complexion and hair style. Babies of 1-2 days clearly recognised their own mothers because they spent significantly more time looking at them. Within 2 days, the baby had learned the perceptual features of his/her own mother's face, a sure example of learning shaped by inborn rules concerning what to pay attention to.

Developmental changes in thinking and learning Jean Piaget13"15 was the first developmental scientist to take seriously the interaction of nature and nurture in children's thinking. He began by studying what he called 'sensory-motor schemas' in infancy. These were part of the baby's biological inheritance and included looking, grasping and sucking. Through careful study of his own children, Piaget concluded that babies did not take in information in a passive way, as a camera might do, but they use environmental information gathered from inborn actions such as looking and sucking to construct a model of the world. For Piaget, learning is not the passive acquisition of information; instead, babies and children actively process information entering through the senses and integrate it into representations of previous information. This means that children do not receive information; they process it in light of what they already know and they integrate it with previous knowledge. Piaget stressed the fact that children are much more than miniature adults with fewer facts at their command. Children perceive and think about the world differently, according to developmental stages. Piaget investigated the regular sequences children follow as they develop concepts. Children all over the world pass cognitive milestones at the same age and even make certain mistakes at the same time. For example, when children learning English discover the '-ed' rule for the past tense, they start to make mistakes they haven't made before. A 3 year old who had been regularly heard to say 'I rode my bike' suddenly changed to 'I rided', incorrectly generalising a new-found rule to irregular verbs. Although grammar varies from language to language, the tendency to over-generalise morphological endings appears in all cultures, showing again an inborn predisposition to pay attention to beginnings and endings in language. Bnhi/i Mtdical Bulletin 1997^3 (No 1)

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Piaget's most important notion is that the child is an active participant in the development of knowledge and constructs his/her own understanding. At each stage in development, the child adapts to the world by using different sorts of mental operations.

Piaget's stages of mental development in young children Sensory-motor stage

During this stage, the infant responds to the world through sensory and motor schemes. The infant lives in the here and now, having little concept of the future, and does not plan. Piaget argued that the child in the period 0-2 years had simple internal representations of the outside world. The child lives in and acts on the world but does not reflect on it. Although recent research suggests that babies can be planful in searching for things and that they may know more about objects than Piaget originally thought, most psychologists agree that thinking in the preverbal child is oriented to the here and now, especially to the child's own view of things.

Pre-operational stage

During the years 2-6, Piaget claimed that language lifted children's thinking to a new level. In this stage, children begin to pretend, to plan events in the future and to interrogate their own past experiences in a systematic way. Piaget described the thinking of children in this stage mostly by things they could not yet do: they were not good at taking the points of view of others; they were not good at classifying things into hierarchical groupings, and they tended to understand or measure things according to appearances rather than underlying mathematical principles.

Concrete operations stage

At about 6 years of age, children abandon their egocentric and nonlogical thought as they develop an organised system of scientific and mathematical concepts. 190

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The lasting impact of early learning We turn to the evidence which supports the widely held belief that early learning in the stages just described has lasting impact. Early learning is considered first inside the home and next as it occurs in day care or nursery school.

How the family environment shapes children's learning

Hundreds of studies have explored the relationship between social background and children's intellectual attainment. Broman et alu, studied more than 50,000 children born in the US and found, not surprisingly, that the average IQ of children rose with both social class and maternal education. British studies show the same17-18. The more interesting questions concern just how certain parents and families create a stimulating and empowering environment. (The influence of genes on this topic is discussed elsewhere.) Broman et at16 showed clearly that the powerful influence of maternal education on children's IQ can be detected after taking into account social class; in other words, the mothers with more education had children with higher IQs within each social class. How do parents help or hinder their children's learning? Bee19 summarises five dimensions of family interaction and stimulation which make a difference to children's learning. Researchers have found that parents of children with high IQ's seem to do the following: 1. They provide the child with an interesting and complex physical environment which includes toys appropriate for the child's developmental level20'21. 2. They are emotionally responsive to the child and involved in their daily lives. This can be seen in their warm, contingent reactions to the child. They smile when the child smiles, talk when the child talks and answer the child's questions22"24. 3. They talk to their child, using language that is accurate and richly descriptive5. 4. They are not excessively restrictive or punitive. Instead they give the child room to explore and even to make mistakes21*25. 5. They have high expectations for their child's learning and emphasise achievement, especially educational achievement26. Two decades ago, researchers discovered the 'structural' influences on children's learning and attainment, e.g. social class, ethnicity or maternal Bntit/i MtdKal Bvlhttn 1997;53 (No 1)

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education. Now they have developed techniques involving fine grained analysis to specify the activities and objects inside the home which seem to make a difference.

Research on learning in preschool settings

The American project, Head Start, has received government funding for two decades in hopes that it would 'break the cycle of poverty'. Initial evaluations seriously underestimated the value of the programme by focusing on measures of intelligence as the main outcome. Sadly they found that early IQ gains quickly washed out, leaving graduates of Head Start no different from control children. Recent evaluations have employed sophisticated research methods to look at a wide array of child outcomes from early education. In 1985, a synthesis of research findings was published27 which combined into a single meta-analysis the results of 210 studies evaluating the impact of Head Start. To enable comparison amongst the studies, findings were converted to statistical 'effect sizes' and comparisons were made across different sites and target groups. McKey and his colleagues concluded that Head Start had immediate, positive effects on children's cognitive ability27. Unfortunately, the 192

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cognitive gains were no longer apparent after the end of the second year at school (see Fig. 2). Head Start also had short-term positive effects on children's self-esteem, scholastic achievement, motivation and social behaviour, but these advantages also tended to disappear by the end of the third year in school. The smaller, better controlled studies of the effects of Head Start have produced more positive findings. A well designed study by Lee et al28 compared the outcomes of 969 disadvantaged children who had experienced three different pre-school environments; Head Start, some other pre-school programme and no pre-school. Large, initial differences on a wide range of outcomes were found at school entry, with Head Start children lower on almost all measures. After adjusting for initial scores (because the Head Start sample were lower), Head Start children showed larger gains on measures of social and cognitive functioning ('readiness for school'20) compared to children in the other two groups. It was not surprising that children in Head Start began school with lower scores because Head Start children tend to be drawn from families of low levels of income and education. Thus, in Lee's study28, Head Start was effective in 'closing the gap' but did not succeed in doing so completely because its children began at greater levels of disadvantage. Notable in Lee's study28, were the large gains made by black children in Head Start. In many evaluative studies of pre-school it has been shown that pre-school intervention is particularly effective for the most economically disadvantaged children29. Black children gained more than white children, even when controlling for initial levels of ability. Further, black students of below average ability gained more than their counterparts of average ability. They concluded that their study demonstrates the effectiveness of Head Start: 'not only were those students most in need of pre-school experience likely to be in Head Start programs, but also that those black students who exhibited the greatest cognitive disadvantage at the outset appeared to benefit most from Head Start participation' (p. 219). There is cause for optimism when examining research on the effectiveness of pre-school programmes which are of 'high quality'. A group of American researchers carried out a meta-analysis of the effects of compensatory education on well resourced, 'quality' programmes. They ignored the garden-variety programmes (which included Head Start) and focused instead on projects of excellent curricular quality and rigorous research design. Lazar et al30 restricted their analysis to 11 carefully monitored programmes, using a statistical analysis enabling researchers to compare effect sizes across many different studies. The researchers located approximately 2000 pre-school 'graduates' and their matched controls to describe their educational and employment histories. In addition they interviewed the youth and their families. Bnttth Medical BuHef.n 1997,53 (No 1)

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Results from the 11 studies showed that attendance at excellent, cognitively oriented pre-school programmes was associated with later school competence at the age of 19 and reduced likelihood of assignment to 'special' education. Interviews carried out at age 19 showed the families of the nursery group to have higher aspirations for their children's employment. The most carefully controlled of the 11 programmes reviewed by Lazar was the Perry Pre-school Project, which became known later as High/Scope. This curriculum is of exceptionally high quality, and it includes a complex training scheme for staff and sound parent participation. The programme has been subjected to careful evaluation for almost 30 years and has consistently shown striking results. Although an initial IQ advantage for pre-school graduates disappeared by secondary school, there were startling differences in outcome between the 65 children who attended the half-day educational programme over 2 years and the control group of 58 children who had remained at home. Figure 3 summarises the findings at age 27 when the High/Scope 'graduates' had: • significantly higher monthly earnings at age 27 (29% vs 7% earning $2,000 or more per month) • significantly higher percentage of home ownership (36% vs 13%) and second car ownership (30% vs 13%) • a significantly higher level of schooling completed (71% vs 54% completing 12th grade or higher) • a significantly lower percentage receiving social services at some time in the past 10 years (59% vs 80%) • significantly fewer arrests by age 27 (7% vs 35% with 5 or more), including significantly fewer arrested for crimes of drug taking or dealing (7% vs 25%) Schweinhart and Weikart31 carried out a cost-benefit analysis which showed that for every $1000 that was invested in the pre-school programme, at least $7160 (after adjustment for inflation) was returned to society. These calculations were based on the financial cost to society of juvenile delinquency, remedial education, income support, and joblessness — set against the running costs of an excellent pre-school programme.

The effects of day care on children's outcomes

Most research studies have looked at the effects of day care on children's emotional adjustment, especially their attachment to their mothers32-33. 194

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High/Scope Perry Preschool Study: Outcomes at age 27 High School Grades Five or more arrests $2000+ Eamings/Mtri Soc Serv since 18

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Several American scholars claim that early entrance into day care, before the age of 1 year, is detrimental to children's emotional development6, but others claim that early entry to day care will not harm children whose parental attachments are secure34. The debate rages on. Research from Sweden tells a very different story; Andersson35 found day care experience gave children a better start in school. He examined the development of 128 children who attended well resourced neighbourhood day care centres. Progress was monitored from the children's first year in day care to the age of 13. No developmental disadvantage was found in the day care group compared to children who had stayed at home. In fact, the highest performance in school tests and the best emotional adjustment was found in the children who had experienced the MOST day care, even before the age of 1 year. Why do Swedish children appear to benefit from attendance at child care centres when some American studies suggest that day care attendance may lead to poor social and emotional adjustment? Perhaps the answer lies in different social policies, with Sweden offering highly subsidised day care to families from all walks of life and the US offering private lower-quality care. Howe36 studied 80 children in deliberately contrasting care in the US. Half were enrolled in excellent centres and half in poor ones. 'High quality' centres were characterised by the following: (i) stable child care arrangements such that children interacted with just a few primary caregivers in any one day; (ii) low staff turnover so that children were cared for by the same individuals over several years; (iii) good staff training in child development; and (iv) low staff:child ratios, e.g. from 0-12 months the ratio was 1:3, from 1-3 years the ratio was 1:4, and from 4-6 years the ratio was 1:8-12. Bnfufc AWica/BuH.hn 1997,53 (No 1)

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In Howe's research, outcomes were controlled for family background and individual differences, factors that might affect development as well as the quality of care36. After controlling for these, children enrolled in the higher quality centres still did better in primary school on both educational and social measures. The picture was different in the low quality centres, with children doing particularly poorly at school when they had been enrolled in lower quality centres before their first birthdays when they entered primary school. These 'early entry' children were distractible, low in task orientation and had considerable difficulty getting on with peers. Research in both the US and Sweden shows clearly that day care, when of high quality, does not harm children's development and may enhance children's learning. There have now been many studies confirming the fact that the higher the quality of day care, the better the learning outcomes for children37"40.

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17 Douglas J The Home and the School. London: MacGibbon and Kee, 1964 18 Osborn AF, Millbank JE. The effects of early education: A report from the Child Health. Contemporary Issues in the Early Years. Paul Chapman Educational Series, 1992 19 Bee H. The Developing Child. New York: Harper Collins, 1995 20 Caldwell B. All day kindergarten: assumptions, precautions and overgeneralisanons. Early Child Res Q 1970; 4: 261-6 21 Bradley RH, Caldwell BM, Rock SL et al. Home environment and cognitive development in the first 3 years of life a collaborative study involving six sites and three ethnic groups in North America. Dev Psychol 1989; 25: 217-35 22 Barnard KE, Hammond MA, Booth CL, Bee HL, Mitchell SK, Spieker SJ. Measurement and meaning of parent-child interaction. In: Morrison JJ, Lord C, Keating DP (Eds). Applied Developmental Psychology. San Diego- Academic Press, 1989; vol. 3; 40-81 23 Bradley RH, Caldwell BM. 174 children: a study of the relationship between home environment and cognitive structure during the first five years. In: Gottfried AW (Ed) Home Environment and Early Cognitive Development: Longitudinal Research. New York: Academic Press, 1984; 5-56 24 Lewis MD. Early socioemononal predictors of cognitive competence at 4 years. Dev Psychol 1993; 29. 1036-45 25 Olson SL, Bates JE, Kaskie B Caregiver-infant interaction antecedents of children's school-age cognitive ability. Memll Palmer Q 1992; 38: 309-30 26 Entwistle DR, Alexander KL. Beginning school math competence: minority and majority comparisons. Child Dev 1990; 61: 454-71 27 McKey RH, Condelli L, Granson H, Barrett B, McConkey C, Plantz M. The impact of Head Start on children, families and communities (final report of the Head Start Evaluation, Synthesis and Utilization Project). Washington, DC: CSR 1985 28 Lee V, Brooks-Gunn J, Schnur E. Does Head Start work? A one-year follow-up comparison of disadvantaged children attending Head Start, no pre-school, and other pre-school programmes. Dev Psychol 1988; 24: 210-22 29 Zigler EF. Formal schooling for four-year-olds? Am Psychol 1987; 42: 254-60 30 Lazar I, Darlington R. The lasting effects of early education: a report from the consortium for longitudinal studies / Soc Res Child Dev 1982, 47: 195 31 Schweinhart LJ, Weikart DP. A summary of significant benefits: The High/Scope Perry PreSchool Study through age 27. High Scope, 1993 32 Clarke-Stewart A. The social ecology of early childhood. In: Eisenberg N (Ed) Contemporary Topics in Developmental Psychology. New York: Wiley, 1988; 292-318 33 Kagan J, Kearsley R, Zelazo P. Infancy: Its Place in Human Development. Cambridge, MA: Harvard University Press, 1978 34 NICHD Infant child care and attachment security: results of the NICHD study of early child care Paper presented at International Conference in Infant Studies Providence, RI, April 1996 35 Andersson B. Effects of day-care on cognitive and socioemononal competence of thirteen-yearold Swedish children Child Dev 1992; 60: 857-86 36 Howe C Can the age of entry into child care and the quality of care predict adjustment in kindergarten? Dev Psychol 1990; 26: 292-303 37 McCartney K. Effect of quality of day care environment on children's language development. Dev Psychol 1984; 20: 244-60 38 McCartney K, Scarr S, Phillips D, Grajek S. Day care as intervention: comparisons of varying quality programs. / Appl Dev Psychol 1985; 6- 247-60 39 Philips D, McCartney K, Scarr S. Child-care quality and children's social development. Dev Psychol 1987, 23: 537-43 40 Schhecker E, White DR, Jacobs E. The role of day care quality in the prediction of children's vocabulary. Can] Behav Sci 1991; 23- 12-24

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