What Makes a Difference Early in Life?
In this section, we introduce the life-cycle model. We then provide a brief review of what we know about early influences on health, behavior, and learning, establishing the following:
• Child development starts at conception, influenced by prenatal health and intrauterine environment, and these factors have important longer-term effects, according to evidence from test of the fetal origins hypothesis.
• Brain development differs between rich and poor children from conception onward.
• Health status, health care access, and parenting are the keys to successful early child development (after birth but before formal preschool).
• Poor health and bad birth outcomes make it harder for such children to catch up with others as life progresses according to the “dynamic complementarity” hypothesis.
• Difficulties persist in providing high-quality preschool experiences for poor children.
Gates and Gaps and the Life-Cycle Model
In a recent pair of cross-national research volumes, the authors and editors took the life-cycle approach to studying the relationship of parental education and income to child outcomes from birth to age 30 (Smeeding et al. 2011a; Ermisch et al. 2012). Figure 8.1 summarizes their model of the process from birth to adulthood for one generation, moving across six life stages from origin (parental socioeconomic status, or SES) to destination (children's adulthood SES). Parental investments and social institutions affect each step, where intermediate gains or losses are measured in multiple domains.
This structure allowed us to combine evidence from different cohorts at different times, with every outcome in every country being ranked by adult educational differences. Taken as a whole, these studies suggest a powerful effect of parental SES on child outcomes in health, cognitive testing, sociobehavioral outcomes, school achievement, and adult social and economic outcomes. Examination of standardized outcomes across 11 countries found a definite and universal pattern: the higher
Fig. 8.1 A model of intergenerational transmission of advantage by life stage (Ermisch et al.2012)
the adult SES as measured by educational attainment, the larger the positive effect on children's outcomes as they crossed each transition point.
The gaps among children ranked by parental education were observed from birth onward and did not diminish as they got older. Although in some cases the gaps widened, this was not always the case. Notably, the slopes of the relationships between parental SES and child outcomes were most steep in the United States.
The same structure facilitates the assessment of how various cohorts of United States children will be affected by growing gaps in parental SES (education, earnings, wealth, and income). In this chapter we concentrate only on the first two stages in Fig. 8.1: conception and birth through early childhood.
-  But not all the steps were filled in for any one country, save Sweden, where the paper by Mood et al. (2012) covers all the steps in the life course. In the larger study, most outcomes were measured for only one cohort. For more, see Ermisch et al. (2012), especially Chap. 2.
-  In this review we draw heavily on recent reviews of the child development literature by Aizer and Currie 2014; Magnuson and Duncan 2014; Heckman and Mosso 2014; Duncan and Magnuson 2013.