Socio- economic status (SES)

SES describes an individual or family ranking on a hierarchy according to access to resources such as wealth, power or social status, education or occupational prestige (Bornstein & Bradley, 2014) and is a component often examined when predictors of academic achievement are studied.

SES in this thesis is limited to parental education level, and the words SES and parental education are used interchangeably. A meta-analysis of over 100,000 students found a relationship between parental education and academic achievement of a medium effect size (r. = .27.95% CI [.23, .39]) (Sirin, 2005). The effect size was moderated by academic outcome, with a larger correlation between parental education and verbal abilities than general academic outcome. Additionally, in a synthesis of a large body of research, Hoff (2013) concluded that children from low-SES homes have lower language skills than children from middle-SES homes. Children from low-SES homes lagged behind their middle-SES peers in a range of language abilities involving vocabulary size, grammatical development, narrative skills, phonological awareness and speed of language processing. Thus, the effects of SES on children’s early language skills are large, pervasive and robust (Hoff, 2013).

However, SES is argued to be a proxy for something, representing a spectrum of many factors that may most likely may have causal effects on children’s learning outcomes Kirby & Hogan, 2008). It is often

claimed that the SES effect is caused partly by parents directly providing resources at home for their children and indirectly by providing the social capital necessary to succeed in school. Common explanation factors are that qualities within mother and child dialog and the amount of storybook reading differ from one SES class to another (Hart & Risley, 2003; Hoff, 2006; Huttenlocher, Waterfall, Vasilyeva, Vevea, & Hedges, 2010;

Rowe, 2012). Furthermore, parents with low SES living in poverty have less access to nutrition and health care (Black et al., 2017). Another explanation is that parents’ beliefs and behaviours differ for different SES classes (Davis-Kean, 2005). All these factors can cause different developmental patterns in children from different SES classes.

Nonetheless, the importance of quality differences in parent-child interaction and basic living standards over the “poverty line” as the main explanation for why SES differences impact language outcomes has recently been challenged by, for instance, the study of Puglisi, Hulme, Hamilton, and Snowling (2017). Based on their findings, they argue that the relationship between home literacy activities and children’s language and reading skills is largely accounted for by maternal skills and may reflect genetic influences. In fact, after controlling for variations in maternal language and phonological skills, Puglisi et al. (2017) find that storybook exposure is not a significant predictor of children’s outcomes.

Other studies find that environmental influences do matter, yet not as much as parents’ genes. For instance, a review by Olson, Keenan, Byrne, and Samuelsson (2014) finds that although environmental influences are generally statistically significant for reading disabilities, the average influence of genes is twice as strong as that of (shared) environmental influences. The meta-analysis of de Zeeuw, de Geus, and Boomsma (2015) also points to the importance of parents’ genes and concludes that genetic variation is an important contributor to individual differences in educational achievement. They find the heritability of reading to be 73%

for reading, 66% for language and 49% for reading comprehension.

Notably, environmental influences accounted for only 10% of variance

in reading, 13% of reading comprehension and 15% of language. Thus, the mechanism that underlies SES as a moderator of academic outcomes seems to be complex.

International and national studies find that the population of minority language-speaking children is over-represented in the national statistics of low-SES families (Barne- likestillings- og inkluderingsdepartementet, 2012; Capps et al., 2005). Fifty-one percent of the children living in poverty in Norway during 2011-2013 were children of minority language-speaking immigrants (Justis- og beredskapsdepartementet, 2015). It has been argued that the low SES of minority language-speaking students could be causing the achievement gap (Bakken, 2003).

It is therefore common to statistically control for SES when comparing monolingual and bilingual learners’ language and reading abilities (e.g., Bakken & Elstad, 2012; Kieffer, 2012a; Strand, Wagner, & Foldnes, 2017).

A recent meta-analysis finds that the differences in oral language skills between monolingual and bilingual children in the instructional language were larger for children from low-SES backgrounds than for children from high-SES backgrounds (Melby-Lervåg & Lervåg, 2014). However, importantly, when SES was controlled for, the group differences were moderate to large. This is in line with the large-scale longitudinal ECLS-K study results of Halle et al. (2012), who find low-SES bilingual children less likely than their bilingual peers of higher SES to be proficient in English before entering kindergarten.

To date, bilingual children from low- and middle-class SES backgrounds have been the main focus of research. A critical review of knowledge of bilingual learners’ literacy and language skills identifies a lack of large-scale studies of high-SES bilingual children’s language and reading development (Hammer et al., 2014). The relationship between high-SES bilingual children’s SES background and language skills is therefore uncertain. However, because there is a relationship between bilingual

learners’ SES and academic outcome (Sirin, 2005), although not as strong as for monolingual learners (Hermansen, 2009, 2013; Sirin, 2005;

Steffensen & Ziade, 2009), one should expect the gap in language skills between monolingual and bilingual learners’ language skills in the instructional language to be smaller for high-SES children. This is supported by findings in the “Miami” study, one of the few studies with a large sample of high-SES bilingual learners (Oller, Jarmulowicz, Pearson, & Cobo-Lewis, 2011). Unpublished findings from the National Household Education Survey of 2001, although measuring different skills, present an even more optimistic view (Woodard & Rodman, 2007). The researchers suggest that SES for bilingual learners works as a mediating factor of cognitive development. In a conference paper, they indicate that a high SES level could work as a threshold value and enable the high-SES bilingual child to outperform the high-SES matched monolingual child in basic math and reading skills.