Early life stress with IQ-achievement discrepancy

Today, I present an article available in full text. Schuurmans, Luik, de Maat, Hillegers, Arfan & Cecil (2022) published “The Association of Early Life Stress with IQ-Achievement Discrepancy in Children: A population-based study” in Child Development. Here are edited excerpts:

Early life stress (ELS) is associated with lower IQ and academic achievement; however, it remains unclear whether it additionally explains their discrepancy. In 2,401 children (54% girls, 30.2% migration background) from the population-based study Generation R Study, latent factors of prenatal and postnatal (age 0–10) ELS were estimated, and IQ-achievement discrepancy (age 12) was quantified as variance in academic achievement not explained by IQ. Results point to ELS as a potential prevention target to improve academic potential.

Intelligence quotient (IQ) facilitates knowledge acquisition and is associated with greater academic achievement for most children (Borghans et al., 2016). However, some children show a discrepancy between their IQ and academic achievement (Borghans et al., 2016; Reis & McCoach, 2000), that is, their school performance differs relative to what would be expected based on intelligence. This IQ-achievement discrepancy could either manifest as higher or lower academic achievement than expected. The latter can be considered particularly detrimental, as it indicates that children are not meeting their full potential, sometimes referred to as academic underachievement. Understanding what factors drive the IQ-achievement discrepancy is important, as lower academic achievement than expected based on IQ has been shown to hamper self-actualization; it is associated with a range of adverse long-term consequences, including delinquent behavior, social problems, lower quality of life, and poor employment prospects (Hoffmann, 2020; McCall et al., 1992).  However, except for some evidence suggesting executive function might be particularly important in the IQ-achievement discrepancy (Alloway & Alloway, 2010; Ng & Hodges, 2020), little is known about what other factors underlie the IQ-achievement discrepancy.

Early life stress (ELS) describes an individual's exposure to single or multiple adverse events in prenatal life and childhood, leading to prolonged phases of stress (Lupien et al., 2009; Pechtel & Pizzagalli, 2011).  Robust evidence shows that exposure to prenatal (i.e., the fetal period) and postnatal (i.e., from birth onwards) ELS is harmful and predicts poor developmental outcomes on a social, emotional, and behavioral level (de Maat et al., 2021; Kingston et al., 2012; Liming & Grube, 2018). A number of individual prenatal and postnatal stressors have been linked to academic achievement and IQ separately (e.g., poverty and childhood maltreatment; Kaya et al., 2016; Young-Southward et al., 2020).  

Information from children and their caregivers was obtained from The Generation R Study, a population-based prospective cohort from fetal life onwards (Kooijman et al., 2017). In short, pregnant mothers within Rotterdam, The Netherlands, were eligible to enroll in The Generation R Study if they had a delivery date between April 2002 and January 2006. In total, 9,778 mothers were enrolled. The study sample is largely representative of the underlying population, although included participants are more likely to have a higher educational level and income. These mothers, their partners, and their children took part in a diverse array of assessments, including behavioral, cognitive, and sociodemographic measures.

This study aimed to characterize the role of ELS in the IQ-achievement discrepancy, using prospective data from a population-based study spanning pregnancy to late childhood. We highlight three main findings. First, we found that ELS was associated with a larger IQ-achievement discrepancy, specifically lower achievement than expected based on IQ. Consistent with prior research, ELS was also individually associated with lower IQ and lower academic achievement in childhood. Second, we found that ELS from both developmental periods emerged as significant predictors of IQ-achievement discrepancy (birth up to age 10). Third, overall ELS (modeled as a latent factor capturing shared variance between ELS domains) showed stronger associations with child outcomes than any individual ELS domains. Together, our findings point to prenatal and postnatal ELS as a significant predictor of IQ-achievement discrepancy, with effects largely driven by the shared variance between ELS types.

The present findings demonstrate that ELS is prospectively associated with a larger IQ-achievement discrepancy around age 12—a critical period of transition between middle and high school. Specifically, ELS is associated with lower academic achievement than expected based on IQ (i.e., underachievement), an important predictor of poor outcomes later in life. Conversely, the odds of overachieving were lower when ELS was higher. According to the effect size guidelines for research in individual differences, our effect sizes were typical to relatively large. This, and the finding that associations remained consistent across several sensitivity analyses, added confidence to our findings. We further confirm previous work by showing that ELS is also associated with both outcomes separately. Of note, recent evidence suggests that the effects of ELS on cognitive outcomes can persist beyond childhood, associating, for example, with cognitive reserve later in life (Lesuis et al., 2018).  Cognitive reserve refers to the individual differences in cognition that help to explain differential susceptibility to brain aging, pathology, or insult (Stern et al., 2020), therefore being considered an important construct for health later in life. Interestingly, cognitive reserve in adults has often been measured as the discrepancy between actual and predicted cognitive achievement (Stern et al., 2020), which parallels how the IQ-achievement discrepancy is measured in children. Consequently, it could be possible that the association between ELS and cognitive reserve—indexed as the IQ-achievement discrepancy—might emerge as early as in childhood. 

In the current study, we show that both prenatal and postnatal ELS are negatively associated with the IQ-achievement discrepancy, and with IQ and academic achievement separately. Although the mechanisms behind prenatal and postnatal associations might be heterogeneous, we found that ELS during both periods relates to a higher risk of poor cognitive and academic outcomes. Interestingly, we found that the effect of postnatal ELS was somewhat stronger than the effect of prenatal ELS. Potentially, prenatal ELS is associated with academic achievement indirectly, by predisposing the child to higher postnatal ELS. However, both periods comprise of items specific to the developmental timing of ELS, to which end prenatal and postnatal ELS are not fully comparable. 

Concerning the type of ELS examined, we found that global prenatal and postnatal ELS (measured as a latent score capturing shared variance across stressors) is associated with child IQ, academic achievement, and the IQ-achievement discrepancy more strongly than any individual ELS domain. Indeed, although individual ELS domains were found to be associated with outcomes when examined separately, associations were substantially attenuated when these domains were modeled simultaneously, suggesting that these associations are mainly driven by shared variance across stressors. This is in line with previous research, showing that early life stressors co-occur and that the shared variance amongst these stressors is associated with poorer child functioning, following a dose-response gradient. Together, these findings underscore the importance of comprehensively assessing stress exposures and accounting for their co-occurence, as focusing on single risks may lead to overestimating the effects of any specific exposure. The interrelatedness of stress domains also illustrates how ELS may act as a cascade of events, in which stressors seem to follow up on each other, with potential cumulative effects. Future research is needed to delineate the mechanisms behind co-occurrent stress and how to target this in intervention and prevention.

Our findings have two main implications. First, they suggest that early screening of ELS may help identify those at highest risk for academic underachievement, an important marker of later life outcomes, including delinquency, social problems, lower quality of life, and poor employment prospects. More specifically, in children known to be exposed to ELS, teachers can be more vigilant to academic underachievement, monitor the IQ-achievement discrepancy, and also offer support more quickly when adverse consequences present themselves. Second, our findings also indicate that academic underachievement is most strongly associated with the co-occurrence of stressors, rather than any individual type of stressor. As such, the implementation of more comprehensive screening tools for ELS is warranted, as assessment of individual stressors in isolation is likely to underestimate effects on IQ-achievement discrepancy. Besides early screening for risk detection, implications for prevention and intervention will depend on whether the association between ELS and IQ-achievement discrepancy is causal, which we are not able to establish from the current study. If a causal role of ELS is supported by future research, this would suggest that primary prevention may help reduce underachievement. Furthermore, intervention strategies may help dampen the impact of ELS on IQ-achievement discrepancy. 

In summary, in this prospective, population-based study we identify ELS, measured both prenatally and postnatally, as a developmental risk factor for the IQ-achievement discrepancy. Specifically, ELS beginning as early as in utero was found to be associated with lower academic achievement than would be expected based on IQ. Early life stressors often co-occurred and showed high continuity over time, with effects primarily driven by shared variance across stress domains. Together, these findings point to ELS as an important prevention target in order to help children reach their full academic potential.

I thought this article was worth presenting with extensive information because it is a large sample and well done study. It seems to me that, as the numbers of at-risk families grows in the US, the number of babies at risk for early life stress will inevitably grow. Although I don’t love IQ testing in general, the focus on discrepancy between IQ predictions and achievement is important.