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, 203), and apparent cross-culturally (Bradley et al., 996). The magnitude of SES-related effects is apparent in studies such as that by Wahlsten (997) who, by examining adoption studies, found that improving SES can improve intelligence: IQ gains of 26 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 (202) 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, 982). Parcel & Menaghan (990) 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. (999) 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 (977) 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 (99), who found there to be substantial SES differences in language performance which is apparent early in a childs 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., 200), which may limit cognitive growth and opportunity of benefitting from school (Bloom, 964). 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.