Creating broader environmental measures
We applied exploratory and confirmatory factor analysis (see Methods) to derive broader composite measures of the family environment that could reflect the correlation between multiple aspects of the neighbourhood and home environment (see Supplementary Figs. 1–10 and 14–24; Supplementary Note 4). From these analyses, we extracted the following higher order dimensions of the family environment.
Supportive parenting. At age 7, we created a measure of supportive parenting, which was constructed as the mean composite of two parent-rated scales: (1) Positive parental feelings (reversed when necessary) and (2) a reverse-coded composite of the harsh parental discipline scale.
Harsh parenting and chaos. Based on our exploratory and confirmatory factor analysis results (see Supplementary Figs. 20 and 21), we extracted a measure of “harsh parenting and home chaos”. This factor loaded three scales: (1) negative parental feelings, (2) harsh parental discipline and (3) chaos at home. We found a great deal of consistency in model fit across different informants and ages; therefore, we created this broad composite of harsh parenting and chaos for both parent and child-reported family environments at ages 9 and 12. We exported factor scores for these four dimensions (Parent and self-reported harsh parenting and chaos at age 9 and Parent and self-reported harsh parenting and chaos at age 12).
Supportive home environment. Based on our exploratory and confirmatory factor analysis results, at age 9, we also extracted a broader factor that we called “supportive home environment” on which loaded three parent-reported measures: (1) a composite score of the stimulating home environment scale, (2) household income, and (3) parental marital status (see Supplementary Fig. 20).
Parental monitoring and chaos at age 16 were constructed as a mean composite of two self-reported scales of parental monitoring and chaos at home, which correlated moderately negatively (r = -0.23) (Supplementary Fig. 22).
Quality of the neighbourhood. The results of exploratory and confirmatory factor analyses (see Supplementary Figs. 5–7) led to the creation of six latent composites that measured broader aspects of the neighbourhood environment: (1) occupancy rating (2) health ratings, (3) household size, (4) population in households, (5) qualification level, and (6) pollution level.
These broader dimensions of the family environment were taken further into our main analyses. However, analyses were also conducted on each individual environmental measure (Supplementary Information). Descriptive statistics of all measures are presented in Supplementary Table 2.
Family environments correlate with polygenic scores for educational attainment (EA), cognitive (Cog) and noncognitive (NonCog) skills.
Consistent with previous work (33, 34), we found that PGSs correlated with academic achievement across development and that associations became stronger over the course of compulsory education, particularly for the EA and NonCog polygenic scores. For example, the correlation between the EA PGS and academic achievement increased from 0.20 at age 7 to 0.36 at age 16 (Supplementary Table 5). Correlation between individual family environmental measures and academic achievement are presented Supplementary Tables 6a-7d.
When examining the association between PGSs and family environments, we observed the strongest positive associations with family socioeconomic status (SES), measured when the twins were 7 years old (e.g., EA, r = 0.31, p < = 0.001, 95% CI [0.28, 0.34]) and 16 years old (e.g., EA, r = 0.30, p < = 0.001, 95% CI [0.26, 0.35]; see Supplementary Table 3a).
Several other aspects of the family environment were also modestly correlated with all PGSs, for example, harsh parenting and chaos rated by parents (associations with EA were r = -0.16, p < = 0.001, 95% CI [-0.20, -0.12] at age 9 and r = -0.12, p < = 0.001, 95% CI [-0.15, -0.08]; at age 12,) and TV consumption at age 9 (r = -0.18, p < = 0.001, 95% CI [-0.22, -0.13] with the EA polygenic score). The supportive home environment composite at age 9 was also significantly associated with all PGSs (r = 0.24, p < = 0.001, 95% CI [0.20, 0.28] for EA, r = 0.10, p < = 0.001, 95% CI [0.05, 0.14] for Cog and r = 0.20, p < = 0.001, 95% CI [0.16, 0.24] for the NonCog polygenic scores). Correlation coefficients and p values for all environmental measures are reported in Supplementary Tables 3a-3d.
Environmental measures correlate with measures of academic achievement across development.
Environmental composites correlated with academic achievement across development with comparable effect sizes to those observed for the PGSs. For example, the correlation was 0.23, p < = 0.001, 95% CI [0.18, 0.28] between a supportive home environment at age 9 and academic achievement at the same age, and 0.28, p < = 0.001, 95% CI [0.24, 0.31] between family SES at age 7 and academic achievement at the same age (Supplementary Tables 4a-4d).
Family environments mediate PGS effects on academic achievement across development.
Given the associations observed between PGSs, family environments, and academic achievement, we conducted mediation models to examine the extent to which these aspects of the family environment mediated the prediction from genetic disposition to variation in academic achievement over development. We started by examining the role of more distal neighbourhood characteristics and continued to explore the role of aspects of the home environment more proximal to each child.
Home environments
We next examined whether more proximal aspects of the family environment could account for part of the genetic effects on academic achievement over development. We examined the role of family environmental contexts at multiple levels of granularity, moving from broad constructs that reflected commonalities across environmental measures to specific indices of the environmental contexts (55).
Figure 2 presents the results of mediation analyses for broader measures of the family context, including SES, supportive home environment and harsh parenting and chaos. When considering the pathway from the EA PGS to academic achievement over development, we found significant mediating effects for most environmental contexts, except for child-rated harsh parenting and chaos at age 9. The strongest indirect effects were found for SES at age 7 (ß = 0.07 [95% CI, 0.06–0.08]) and age 16 (ß =0.11 [95% CI, 0.09–0.13]), when SES mediated nearly 1/3 of the EA PGS prediction. Supportive home environment at age 9 (ß =0.05 [95% CI, 0.03–0.06]) was also found to have a substantial mediating role (~ ¼ of the total prediction). Model estimates are presented in Supplementary Table 9.
Since we found significant mediating effects for the EA PGS, we examined whether these could be captured by cognitive or noncognitive PGSs. Figure 2 therefore shows the mediating effects of the family environment in the prediction from Cog and NonCog PGS to academic achievement over development. Although a similar pattern of results emerged for both Cog and NonCog PGSs, effects were stronger for the NonCog PGS prediction (e.g., the indirect effect of family SES was ß = 0.06 [95% CI, 0.04–0.09] for Cog and ß = 0.09 [95% CI, 0.07–0.12] for NonCog; Supplementary Tables 10a and 10b), particularly when considering them in light of the total PGS effect. Although PGS predictions were weaker for NonCog PGS, mediating effects approached, or even exceeded half of the total PGS effect (e.g., for family SES at age 7; Fig. 2 right panel).
Mediating effects for specific indices of the family environmental contexts were generally weaker, although many environments significantly contributed to the PGS effects on academic achievement at all ages. For example, home chaos across all measurements accounted, on average, for 11% of the total EA PGS effects (see details in Supplementary Fig. 27 and Supplementary Table 11). A similar pattern of results emerged when we repeated the analyses with three other PGSs (for IQ (47), Cognitive and Noncognitive skills (40)). Results are presented in Supplementary Figs. 28 and 29; Supplementary Tables 12 and 13.
Controlling for the effects of SES using a two-mediator mediation model
Considering that SES was the strongest mediator of the PGS prediction of academic achievement at several developmental stages and considering its correlations with several other aspects of the family environment, we tested whether our results were driven by family SES. To this end, we extended our mediation models to include family SES as an additional mediator and run two-mediator mediation models (see Methods). These models allowed us to test whether all other aspects of the family environment remained significant mediators after accounting for the role of family SES. Because family SES was measured at ages 7 and 16, for all models predicting achievement at ages 7, 9 and 12, we included family SES measured at age 7, while for the models predicting achievement at 16, we included a measure of family SES collected when the twins were 16 years old. Although we found that family SES played a significant role in mediating the PGS predictions of academic achievement, the indirect effects of other environmental measures (e.g., harsh parenting and CHAOS and supportive home environment) remained significant, albeit attenuated (Supplementary Fig. 30 and Supplementary Table 13). Similar results were observed across all PGSs and at all developmental stages. (Supplementary Figs. 31 and 32; Supplementary Tables 14 and 15).
Separating mediation effects into between and within-families to further investigate gene-environment correlation.
Given the outcomes of our mediation analyses, which point to widespread gene-environment correlation in academic development, we applied multilevel mediation models (see Methods) to investigate whether family environments mediated the PGS-achievement relationship not only between but also within families, these analyses were only possible for those environmental measures that differed between siblings (see Fig. 3). As expected, PGS effects were attenuated at the within-family level (56). We also observed that nearly all mediation effects were captured at the between-family level for the EA PGS prediction of achievement across development (Fig. 3 and Supplementary Table 16) and consistent for the Cog and NonCog PGSs (Supplementary Figs. 33 and 34; Supplementary Tables 17 and 18), suggesting that children might experience family environments that correlate with their genotypes largely through passive gene-environment correlation processes.