Abstract
This study documents differences in childhood IQ trajectories of Guatemala City children, aged 6–15 years and born 1961–1993, according to school attended, height-for-age Z-scores (HAZ) and over time (Flynn effect). IQ data come from the Universidad del Valle de Guatemala Longitudinal Study of Child and Adolescent Development. IQ was measured using standardised tests from the Otis-Lennon Mental Ability Test-series. A multilevel model was developed to describe 60,986 IQ observations (level 1), in 22,724 children (level 2), in five schools representing students of different socioeconomic status (SES) (level 3). Average IQ trajectories differed by school. The difference in average IQ at age 11 years between the students of high and low SES schools was 28.7 points. A one-unit increase in HAZ was associated with a 1.42 (0.72, 2.11) unit higher IQ if HAZ was <0, this association was stronger in public compared to private schools. Conversely, one unit increase in HAZ was only associated with a 0.3 (0.001, 0.5) unit higher IQ if HAZ was ≥0. With each birth year increase, IQ at age 11 years increased by 0.14 (95% CI 0.12, 0.16) units, although this Flynn effect attenuated slightly across adolescence. We found no evidence of secular change in the inequality in IQ trajectories (according to school or HAZ). Shorter children from disadvantaged schools in Guatemala City have lower IQ than their taller and wealthier peers, possibly reflecting the damaging effects of poor early life environments both for linear growth and cognitive development.
Highlights
Intelligence tests are commonly used to assess cognitive ability, and have utilitarian value because they are reasonably good predictors of grades at school, performance at work, and many other aspects of success in life (Nisbett et al, 2012)
Individual differences in intelligence plateau and remain relatively stable into old age, that is, individuals maintain their relative rank in Intelligence Quotient (IQ) (Deary, 2014; Schalke et al, 2013), Differences in IQ have been reported between socioeconomic status (SES) groups, schools, and by international population comparisons (Ceci & Williams, 1997; Engelhardt, Church, Paige Harden, & TuckerDrob, 2019; Lynn & Vanhanen, 2012; Schwartz, 2015)
Differences in IQ related to the education a child receives and the school they attend have been documented in high-income countries (Ceci & Williams, 1997; Ritchie & Tucker-Drob, 2018)
Summary
Intelligence tests are commonly used to assess cognitive ability, and have utilitarian value because they are reasonably good predictors of grades at school, performance at work, and many other aspects of success in life (Nisbett et al, 2012). Children of lower SES (e.g., according to parental education, income, and occupation) perform on average worse in cognitive tests than children from more privileged homes as early as 2 years of age in the UK, and this inequality continues throughout childhood and adolescence (von Stumm & Plomin, 2015). Differences in IQ related to the education a child receives and the school they attend have been documented in high-income countries (Ceci & Williams, 1997; Ritchie & Tucker-Drob, 2018). Part of the education related differences in IQ are likely due to the background SES of the students themselves, and because lower SES students tend to attend poorer quality schools where differences may be exacerbated (Batty, Der, Macintyre, & Deary, 2006; Becker, Lüdtke, Trautwein, Köller, & Baumert, 2012; Brinch & Galloway, 2011; Ceci & Williams, 1997). No previous study has investigated schoollevel differences in childhood to adolescent IQ trajectories in a low- or middle-income country (LMIC)
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