26 October 2021

Socioeconomic Status v. Intelligence and Parental Ability

At the level of an entire school or school district at the K-12 level, the best predictor of academic achievement is the socioeconomic background of its students.  And, the gaps get bigger as kids get older (something called the Matthew Effect).

Some of this is because people with higher IQ and other socioeconomically valuable psychological traits, which are real things with a strong hereditary component, tend to have more socioeconomic success (which is the main reason why we care about IQ). These people tend to marry each other in this age of assortive marriage, and in turn they have kids who share these traits. And, while IQ doesn't predict everything well, it is an excellent predictor of academic success in school.

Is this purely hereditary model enough? No. Serious socioeconomic, nutritional, and educational deprivation (especially for preschool age and young elementary school aged children) can also undermine academic achievement, even if someone has a high IQ potential. 

But, once you hit a socioeconomic situation which we'd call "middle class" in the U.S. (in its very elastic definition of that term), for someone going to public schools in all but the worst neighborhoods (in terms of academic achievement in schools and personal safety and lead exposure), these deprivation effects become minimal.

A new study concludes, however, that almost all effects on academic ability and achievement attributed to socioeconomic background and the Matthew Effect can be successfully modeled as a combination of the child's inborn ability as demonstrated at a young age, and the nurture derived or not yet realized genetic gains involved in their primary caregiver's abilities modeled here as "mother's ability". 

This is true even though socio-economic gaps in measured academic achievement tend to accumulate and grow over time when not controlling for a child and a mother's academic abilities.

This result tends to support the idea that early, quality, full day preschool is more valuable in the long run for poor children whose primary caregivers have less academic ability (or aren't able to spend time with their children to transmit their ability because they work so much), than for middle class and more affluent children whose have a high ability parent that is a primary caregiver for them in those years. What full day preschool is providing to poor children is higher ability primary caretakers for much of each day than they would otherwise have been exposed to without it. 

This study is at odds with a massive volume of conventional heredity tests that show little or no nurture effects. 

It may be that these nurture effects are masked by homogeneous and correlated nurture effects in most samples. Alternatively, the mother's ability tested in this study may be a proxy for late blooming hereditary ability in the mothers' children. But the "Head Start" studies showing strong benefits from these programs, and non-replication of these results to nearly the same extent in more broadly available full day quality preschool programs, tends to support a primary caregiver nurture, rather than a not yet blossomed inborn ability hypothesis.

Studies that investigate the effects of socioeconomic background (SES) on student achievement tend to find stronger SES effects with age, although there is much inconsistency between studies. There is also a large academic literature on cumulative advantage arguing that SES inequalities increase as children age, a type of Matthew Effect
This study analysing data from the children of NLSY79 mothers (N ≈ 9000, Obs ≈ 27,000) investigates the relationship of SES by children's age for two cognitive domains (Peabody Picture Vocabulary test and digit span memory) and three achievement domains (reading comprehension, reading recognition and math). 
There are small increases in the SES-test score correlations for several domains, but there are more substantial increases in the test score correlations with mother's ability and prior ability. Regression analyses found linear increases in SES effects for all domains except digit memory. However, when considering mother's ability, the substantially reduced SES effects did not increase with children's age. Much of the effects of SES on children's domain scores are accounted for by mother's ability. The effects of prior ability also increase with age and SES effects are small. Therefore, there is no evidence for cumulative socioeconomic advantage for these domains. Generally, increases in SES effects on children's cognitive development and student achievement are likely to be spurious because of the importance of parents' abilities and their transmission from parents to children.

Gary N. Marks, Michael O'Connell, "No evidence for cumulating socioeconomic advantage. Ability explains increasing SES effects with age on children's domain test scores" 88 Intelligence 101582 (September-October 2021) https://doi.org/10.1016/j.intell.2021.101582. 

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