Academic journal article Merrill-Palmer Quarterly

Acquisition of Maternal Education and Its Relation to Single-Word Reading in Middle Childhood: An Analysis of the Millennium Cohort Study

Academic journal article Merrill-Palmer Quarterly

Acquisition of Maternal Education and Its Relation to Single-Word Reading in Middle Childhood: An Analysis of the Millennium Cohort Study

Article excerpt

Early child development in general, and oral language and literacy in particular, are associated with social advantage (Hoff, 2006; B. Hart & Risley, 1995; Maggi, Irwin, Siddiqi, & Hertzman, 2010) with implications for policy (Shonkoff 2007): There is a social gradient (Law, Reilly, & Snow, 2013; Marmot, 2010), as well as resilience, in more disadvantaged families (Schoon, 2006). A number of different mechanisms have been posited for this social gradient in terms of both proximal environment and behavioral genetics, which are likely to be interrelated (Harlaar, Dale, & Plomin, 2007; S. A. Hart et al., 2013; Trzaskowski et al., 2014). Numerous associations have been demonstrated between social disadvantage and language development (e.g., McCormack, Harrison, McLeod, & McAllister, 2011; Taylor, Christensen, Lawrence, Mitrou, & Zubrick, 2013) without establishing causes of observed disparities in populations. Control by randomization in small experimental studies, such as those evaluating Head Start interventions (Barnett, 1998; Heckman, 2013), makes understanding effects representing the full range of social difference very difficult. In general, studies of child-development outcomes account for socioeconomics by using a proxy variable in the analysis, or by matching control groups, understating the strength and breadth of the association with language outcomes observed in large empirical studies.

Socioeconomic status (SES) can be measured as income, housing (type and tenure), occupational status, and parental educational attainment at an individual or a household level, or by proxy of area deprivation. Although relative poverty (i.e., income below the poverty line) is established as a risk factor for negative child outcomes (Huston, McLoyd, & Garcia Col, 1994), poverty alone cannot explain gradients observed higher up the SES scale. For example, parents' economic and social context influences parental attitudes and aspirations, as well as the educational and cultural opportunities for children (Bennett et al., 2009), while resource limitations preclude certain activities beyond the home. The quality and nature of a child's early home learning environment is both strongly associated with their developmental outcomes and influenced by a range of SES factors and cultural practices (Froyen, Skibbe, Bowles, Blow, & Gerde, 2013; Johnson, Martin, Brooks-Gunn, & Petrill, 2008). The availability of books (whether or not for the child to read) is an example, and one that is often described as reflecting cultural capital because it reflects investment in cultural resources.

Behavioral genetics can ascribe a large amount of variation in language ability to heritability (Harlaar et al., 2007; S. A. Hart et al., 2013), implying that environmental intervention has constrained potential beyond the known toxicity of extreme privation. Earlier analyses rest on the zygosity of co-twins, who do not have typical language development (McEvoy & Dodd, 1992), and make further assumptions about the equal environments they experience (Shonkoff & Phillips, 2000; Trzaskowski et al., 2014). Detailed study of language outcomes shows that some aspects of language development are more related to environmental factors than others; specifically, language comprehension appears to be less heritable (Hoekstra, Bartels, van Leeuwen, & Boomsma, 2009). Although it has been proposed that gene-environment interactions could still play a role here, evidence from studies of candidate genes is very weak (Jerrim, Vignoles, Lingam, & Friend, 2015) and Genome Wide Association Study (GWAS) analyses have been unsuccessful in identifying the root of the large heritable component (Tran et al., 2013). There is some suggestion that genes may even influence SES (Trzaskowski et al., 2014), but careful attention to SES measurement and missing data has shown earlier effects to be overstated (Jerrim et al., 2015). Thus, Genetic Complex Trait Analysis (GCTA) is proposed by behavioral geneticists as combining the genetic and SES dimensions to predict cognitive outcomes (Trzaskowski et al. …

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