Growing up in Scotland: the impact of children's early activities on cognitive development

Chapter 2 Cognitive Development

2.1 Introduction

There are many aspects to children's development. These include: their physical growth; the development of social and emotional understanding; the formation of relationships with their carers, wider family and peers; and their cognitive development. This latter aspect itself comprises a number of facets, such as visual perception, memory, language and higher executive functions such as planning and decision making. These developmental achievements are highly interdependent; many of the cognitive functions children acquire depend on a certain degree of maturation within the growing brain before they can be performed adequately, or in some cases, at all. Similarly, children's ability to form words and start to speak is linked to physical changes in the palate and tongue as well as neurological changes within the brain. The Growing Up in Scotland study has included a number of measures designed to capture some of these developmental milestones over the years, ranging from reasonably straightforward measures of height and weight, to somewhat more complex measures of children's motor skills, and more recently, their conceptual understanding. This chapter describes these measures of cognitive ability, outlines their importance for other developmental outcomes, and highlights some of the existing literature about factors influencing cognitive ability.

2.2 Measures of cognitive development

Cognitive ability was measured in the GUS birth cohort at age 34 months via two assessments: the naming vocabulary and picture similarities subtests of the British Ability Scales Second Edition ( BASII). These two assessments measure, respectively, language development and problem solving skills. Each subtest is part of a cognitive assessment battery designed for children aged between 2 years and 6 months and 17 years and 11 months (Elliott, 1996). The assessments are individually administered. Numerous tests of ability and intelligence exist but the BAS is particularly suitable for administration in a non-clinical setting such as within a social survey like GUS.

Hill (2005) provides a useful and succinct history of the development of the BAS and its strengths relative to other measures of intelligence. These strengths include: its development in Britain using a domestic reference population, the fact it is comprised of a number of stand-alone components (surveys rarely have time for lengthy tests to be administered), its theoretical grounding, its explicit concern to measure ability rather than intelligence, and the fact that although versions of the scale can be administered up to the age of 17 years and 11 months each of its age-specific versions were specifically designed for their corresponding age group.

Its origins lie in the 1960s when the then Department for Education and Science in London funded a programme to develop a British Intelligence Scale ( BIS). This was in response to concerns about existing measures of ability that had been developed in America and were therefore felt to have cross cultural limitations. The BIS was designed to be more theoretically driven than previous measures and was grounded in the work of key developmental psychologists at the time (Bruner, Piaget and Kohler). Elliot steered the final stages of its development, during which time the name changed from the British Intelligence Scale to the British Ability Scale, signalling its creators' desire to distance it from the more controversial area of intelligence testing. The first version of the scale was published in 1979 and a further revision by Elliot between 1993 and 1996 resulted in the BASII (Elliott, 1996), as used in the GUS study.

The scales are designed to form a composite measure known as General Conceptual Ability ( GCA) with each subtest contributing towards the overall GCA score. The way in which the GCA is determined depends on the age of the children being tested. In the first phase, which spans the period 2 years and 6 months to 3 years and 5 months (the age range within which the GUS cohort fell at the point of testing), the individual scales contribute directly to the GCA score. At later ages three intermediate cluster scores (measuring verbal ability, non-verbal reasoning and spatial ability) are generated and these then feed into the composite GCA. A key feature of the BAS is that each sub-scale is also suitable for use in its own right. Due to time limitations within the GUS interview only two of the four scales were used so an overall GCA score cannot be calculated. As noted above, the two scales used were the naming vocabulary assessment and the picture similarities assessment.

Naming vocabulary requires the child to name a series of pictures of everyday items and assesses the expressive language ability of children. In the picture similarities assessments children are shown a row of four pictures on a page. They are asked to place a free-standing card with a fifth picture underneath the picture with which the card shares a similar element or concept. The picture similarities assessment measures a child's problem solving ability. There are 36 items in total in the naming vocabulary assessment and 33 items in the picture similarities assessment. However, to reduce burden and to avoid children being upset by the experience of repeatedly failing items within the scale the number of items asked to each child is dependent on their performance. For example, one of the criteria for terminating the naming vocabulary assessment is if five successive items are answered incorrectly.

The analysis reported here used normative BAS scores, derived from the standard BAS tables and defined with reference to the standardisation samples used in developing the assessments. These normative scores were converted into T-scores based on the values in the standardisation sample for the applicable age band. T-scores range from 20 to 80 and have a mean of 50. A child with a T-score of 50 is therefore placed at the mean value for their age. Higher scores on either scale denote an increase in cognitive ability and, conversely, lower scores indicate a reduced level of ability. Table 2.1 presents the mean T-scores for the two scales and shows how the scores are distributed across the population.

The analysis presented in Chapter 4 of this report explores the difference in mean scores at age 34 months according to key socio-demographic factors, patterns of children's activities at age 10 and 22 months, and parents' attitudes towards these activities.

Table 2.1 British Ability Scale Naming Vocabulary and Picture Similarities scores at age 34 months

2.3 Why measure cognitive development?

Previous cohort studies that have included measures of child development have established that early cognitive ability influences later outcomes. For example, analysis by Feinsten (2003) of the 1970 Birth Cohort Study ( BCS) showed that assessments of ability at 22 and 42 months predicted educational outcomes at age 26 years. This analysis also demonstrated that low scoring children from high socio-demographic status families were more likely to have progressed and improved their position in later years than similarly scoring children from more disadvantaged backgrounds who tend to stay at the bottom end of the distribution. The wider research literature also suggests that early poor cognitive ability can have a negative impact on other outcomes in the realms of education, employment, health and social development (Duncan and Brooks-Gunn, 1997; Essen and Wedge, 1978; Rutter and Madge, 1976; Schoon, 2006; cited in Jones and Schoon, 2008). Using cohort studies such as GUS to measure cognitive ability, and how it differs within the population, can help build a better understanding of the dynamics of children's development and to identify stages at which interventions might have a positive influence on later outcomes.

2.4 Factors influencing cognitive development

Previous research has uncovered a number of factors influencing children's cognitive ability that operate at a number of levels. For example, individual differences within children, such as their gender (Jones and Schoon, 2008) and birth weight (Shenkin, Starr and Deary, 2004), other gestational or early development indicators such as head circumference (Silva, Metha and O'Callaghan, 2006) as well as family/household level factors such as income level, ethnicity, parental education and social class (Jones and Schoon, 2008; Silva, Metha and O'Callaghan, 2006). Chapter 4 illustrates the relationships found in this study between a selection of individual and household level factors and children's cognitive ability at age 34 months.

Previous country-level analysis of the second sweep of the Millennium Cohort Study ( MCS) conducted when the cohort members were of a similar age to the children covered in this report suggested that children in Scotland had slightly higher (though statistically significant) ability scores, as measured by the BAS vocabulary assessment, than their counterparts elsewhere in the UK (Dex, 2008). This analysis concluded that differences between the countries could not be explained by socio-demographic factors. However, the results presented here suggest that the ability scores for children in Scotland are closer to the UK average than those found in the MCS Scottish sample. The GUS sample is considerably larger than the MCS sample so it is possible that this apparent 'Scotland effect' was a consequence of the larger sampling error that will be associated with the MCS estimate. As the authors also note, the second sweep of the MCS was subject to differential non-response in Scotland that resulted in the sample having an overrepresentation of more affluent families. Although the previous analysis controlled for a number of possible sources of bias, such as mother's education level and household income, no statistical model can ever account for all sources of bias. This may also have contributed to the previous finding.

There is a large body of evidence that suggests parenting styles and children's activities have a powerful influence on cognitive ability as well as other developmental outcomes (see Lugo-Gill and Tamis-LeMonda, 2008, for an overview of the literature in this area). However, the strong interrelationship between parenting styles, activities and socio-demographic factors - for example parents' willingness to read to their children and their own educational background - means that any analysis that attempts to explore the impact of activities needs to take account of these wider influences. The analysis presented in Chapter 5 of this report does this by exploring the independent effect all these factors have on cognitive ability at age 34 months in an attempt to establish whether children's activities can moderate the well-established effects of socio-demographic factors on children's outcomes. The next chapter outlines the measures of children's activities that will be used in this analysis.