The very first words of this new study by Marks & O’Connell, published in Intelligence are a very clear question:

Does the impact of socioeconomic (SES) on children’s test scores increase as children grow older?

This is such an important issue, as we often have learned that there is a Matthew effect in place, making the gap between poor and rich bigger. The widening of the gap is often a fact, but this new study examined the causes of this widening. And the answer might be different than you think.

The study summarized:

• Data analysed for five domains for children of the NLSY79 mothers study.
• SES effects increase for only some domains and not substantially.
• No increase in SES effects when considering mother’s or children’s prior ability.
• Effects of child’s prior ability on test scores increase substantially with age.
• SES effects are small net of mother’s ability.

The conclusion thus reads:

The main conclusion from this study is that the increase in the SES effects on cognitive development and student achievement as children grow older observed in these data is spurious, confounded by parental and child’s abilities. Increases in SES effects with age for some domains disappear with the inclusion of mother’s ability and mother’s ability age interaction terms, or with analogous measures of prior ability. Net of mother’s and child’s abilities, SES effects on children’s test scores are small, so changes in its effects with age are unimportant.

The main limitation of this study is the absence of a father’s ability. But the authors argue that this would probably mean even a lesser impact of SES. This does sound logical.

Bear in mind: this student doesn’t state that SES doesn’t play a role in the existence of differences, it only discusses the accumulation over time.

Abstract of the study:

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.