Socioeconomic status (SES) is a widely studied concept within the social sciences due to its predictive value with a number of life outcomes. Although much debate has occurred as to exactly what SES represents it is generally quantified as a measure of parental education, family income and occupational status.
Examining the relationship between SES and intelligence has historically proven difficult; with estimates regarding the extent of their association varying between reports. Such disparity may have emerged due to the wider issue in the study of intelligence. As it is a largely latent variable, researchers have used a variety of measures in an attempt to operationalize it, including IQ, academic achievement, or attainment of higher education, which is often inconsistent across studies. Nonetheless, SES is widely found to be significantly implicated with variations in intelligence; with such differences shown to be stable from early childhood to adolescence (Deary, Pattie, & Starr, 2013), and apparent cross-culturally (Bradley et al., 1996). The magnitude of SES-related effects is apparent in studies such as that by Wahlsten (1997) who, by examining adoption studies, found that improving SES can improve intelligence: IQ gains of 12–16 points were made when children transferred from low to high SES families. Many factors have been suggested to be involved in this association, although those which will be discussed in this essay are the impact of family characteristics and home environment, neighborhood environment, stress, and stereotype threat.
Firstly, the relationship between SES and intelligence may be mediated by the distinction in family characteristics and home environment between high and low SES environments. SES-related differences in cognition and achievement are prevalent even before children begin schooling (Heckman, 2006), and continue throughout childhood and adolescence (Bradley & Corwyn, 2002), therefore it seems likely that a stable characteristic throughout development, such as home environment, is responsible for driving this association. Research by von Stumm (2012) suggested one possible reason for this difference to be nutrition, with higher-SES being associated with improved cognitive performance at ages 3 and 5, the effect being partially mediated by having a higher number of ‘slow’ rather than fast food meals per week. Such differences in diet are perhaps reflective of the differing access to resources as a result of SES which, in turn, lead to the observed differences in cognitive ability. Socioeconomic status has also been found to be related to differential parenting, as adults incorporate aspects of their occupational environment into their parenting style (Kohn & Schooler, 1982). Parcel & Menaghan (1990) observed that mothers who encountered a wide variety of tasks and problem-solving opportunities in their work environment provided more warmth, support and volume of stimulating materials to their children, who, as a result, exhibited more advanced verbal competence. However, it seems probable that such occupations are available universally, therefore such an advantage would not be restricted to one socioeconomic class. DeGarmo et al. (1999) found each indicator of SES (income, education and occupation) to be associated with better parenting, in turn affecting school achievement via skill-building activities and school behaviour. For example, Leibowitz (1977) demonstrated that more highly educated (high-SES) mothers were more likely to participate in activities with their children which encourage the development of verbal skills (e.g., reading), when compared to those which would not involve such interaction (e.g., playing video games). This has been further supported by Hoff-Ginsberg (1991), who found there to be substantial SES differences in language performance which is apparent early in a child’s life. The difference in SES observably manifests itself in availability of resources. Low-SES children often lack access to cognitively stimulating materials and experiences, such as visiting libraries, museums, or attending theatrical performances (Bradley et al., 2001), which may limit cognitive growth and opportunity of benefitting from school (Bloom, 1964). It seems probable that the environment in which a child grows up both facilitates and enhances positive effects of specific traits. For example, a child who is naturally verbally gifted who grows up in a high-SES household will be provided with more books to further enhance the ability, an opportunity perhaps missed by low-SES individuals. In this way, socioeconomic status is implicated in the association with intelligence in increasing or decreasing the likelihood that the full potential of the child will be attained. It may not be that underlying intellectual differences are present, rather that the extent to which they can be unearthed is the causal factor in the disparity of measures of intellect.
Such economic inequality between socioeconomic classes is observable at a wider level, creating differences in academic preparation (which exists) at both institutional and familial levels. Parrish, Matsumoto and Fowler (1995) found a significant relationship between higher neighborhood SES and greater school expenditures per student, which itself is associated with significant increases in achievement (Greenwald, Hedges, Laine, 1996). Therefore, it seems plausible that intelligence is influenced indirectly by the neighborhood environments children are exposed to as a function of their socioeconomic status. The increased likelihood of low-SES individuals provided with lower quality schooling is highly detrimental when research has shown that the academic development of socioeconomically disadvantaged children is more strongly influenced by formal schooling than high-SES children, due to a decreased likelihood of experiencing a cognitively rich home and neighborhood environment. They are more likely to encounter larger class sizes (Loeb, Darling-Hammond, & Luczak, 2005), and be surrounded by low-achieving peers. This is highly disadvantageous when considering the positive relationship between peer ability levels and student learning (Hanushek et al., 2003). Overall, it seems those from low-SES backgrounds face multiple barriers to learning; namely, they are disproportionately assigned to ability groups and programs that afford limited resources and opportunities to learn (Ready, 2010). In addition to the quality, the quantity of schooling may also have an impact on intellectual attainment. SES also has an impact on both school attendance and number of total years of schooling completed (Haverman & Wolf 1995, Brooks-Gunn & Duncan 1997), which may be as a result of differing parental expectations - low-SES parents are likely to view a high-school diploma as the norm, while high-SES consider a degree to be the norm. In general, research has shown that exposure to high-quality schooling for an extended period of time – opportunities generally afforded to high-SES individuals - appears valuable in influencing intelligence when defined as educational attainment.
Institutional differences, such as in formal education, cannot entirely account for all the variation in cognition. SES differences in brain development are apparent in attention and working memory before children experience school. There must, therefore, be mediators encountered early on in life, such as exposure to stress. Individuals who are socially disadvantaged or have limited economic resources experience a greater amount of stress over the life course (Taylor and Seeman, 1999), since low-SES families are more likely to experience uncontrollable and destabilizing life events such as family dissolution and household moves (Bradley & Whiteside-Mansell, 1997). Stress in early life, developing as a result of exposure to risky family dynamics can be characterized by conflict‐laden relationships, aggressive and harsh parenting (McEwen & Gianaros, 2010), and has been found to impair intellectual ability and academic performance (Pechtel & Pizzagalli, 2011). This association may be explained by research such as that conducted by Lupien, King, Meaney, and McEwen (2000), who found that children as young as 6 from low-SES backgrounds had significantly higher levels of stress hormones, related to atrophy of brain structures, involved in learning and memory, as well as general cognitive deficits (Lupien et al., 1998). Research showing the brain’s plasticity as a result of experience throughout development adds further weight to the contention that SES influences on the developing brain are plausible. Hackman and Farah (2009) suggest that SES modifies the heritability of IQ: for low-SES families any variance in IQ is largely attributable to environmental influence, as this is the limiting factor in this group, whereas for high SES families, genes account for most of the variance, with environmental influences ‘at ceiling’ level. This proposition is supported by Ready (2010), who found that the effects of schooling on cognitive development are stronger for lower SES individuals, who perhaps have not had the same degree of opportunity to reach their full potential in the environments they experience. Therefore, it seems low-SES individuals are more likely to encounter stress, an abundance of which may cause cognitive deficits, affecting their performance on intelligence tests.
The fourth possible reason for differing intelligence is the impact of stereotype threat. This phenomenon can be described as an instance in which members of a stigmatized group in society, in this case low-SES members, perform more poorly on a standardized tests due to fear of confirming the negative stereotype associated with their in-group. Much research has found that participants routinely judge low-SES individuals as having below-average intelligence, (Miller, McLaughlin, Haddon & Chansky, 1968), and they are routinely described as ‘low-ability’ (Brantlinger, 2003). Spencer and Castano (2007) found that when socioeconomic identity is made salient before taking a test, low-SES students performed significantly worse, reporting lower ratings of self-confidence when compared to performance in non-threatening conditions. Due to fear of confirming a stereotype of intellectual inferiority, intellectual test performance may be impaired. Strengths in such research emerge in the ability to contextually prime SES, which, although not entirely applicate to real-world SES, adds some confidence regarding the causation of the two variables. On a related note, the notion of self-fulfilling prophecies may also be at play concerning a teacher’s explicit expectation of or attitude towards a student. Jussim, Eccles and Madon (1996) found that teacher expectancy effects to be especially strong amongst students from lower socioeconomic backgrounds. In this way, differing intelligence levels are attributed to contextual factors, demonstrating a situationist, or at least situation interactionist, explanation for the academic underperformance (Aronson et al., 1999). It may simply be that the measures of intelligence taken (i.e., standardized tests) are not only measuring intelligence but also the extent to which the individual is affected by the situation. Disparity in test performance as a function of SES may emerge simply because low-SES individuals are disadvantaged from the outset by situational variables.
The most convincing reason for the association between socioeconomic status and intelligence would appear to be the differing home environments, such as contact with cognitively stimulating materials and experiences. Although perhaps perceived as merely a moderator of the effect of socioeconomic status, it seems to strongly contribute to the development of cognitive abilities. It must be mentioned that the results of studies owing to the differences in parenting style between socioeconomic statuses should not be seen as creating sweeping generalizations, as often low-SES environments are able to provide similarly intellectually stimulating environments. Nevertheless, the way that a child is brought up is undoubtedly affected by the economic position of the family, exemplified in availability of resources and experiences. Growing up in a low-SES environment may simply limit one’s access to facilities which promote cognitive development. Early poverty has been shown to be a better predictor of cognitive achievement when compared to poverty experienced in late or middle childhood. Therefore, it appears that the early part of childhood is somewhat of a critical time in determining later intelligence, and what affects later intelligence the most is the extent to which a child’s potential is revealed during this time.
The underlying question which remains is whether intelligence the result of economic and educational opportunities afforded by SES, or due to genetically transferred personal characteristics. It must be acknowledged that when measuring intelligence too much weight is generally given to the effects of SES due to a difficulty in separating the impact of genetic and environmental factors. Nonetheless, family environment and home characteristics provide arguably the strongest explanation for the association, although a combination of all factors seems necessary. The relative contribution of each is perhaps dependent on other uncontrolled for variables, such as geographical location or average level of affluence in a specific area.