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Findings in adults have shown that crystallized measures of intelligence, which are more culturally sensitive than fluid intelligence measures, have greater heritability; however, these results have not been found in children. The present study used data from 8,518 participants between 9 and 11 years old from the Adolescent Brain Cognitive Development (ABCD) Study. We found that polygenic predictors of intelligence test performance (based on genome-wide association meta-analyses of data from 269,867 individuals) and of educational attainment (based on data from 1.1 million individuals) predicted neurocognitive performance. We found that crystallized measures were more strongly associated with both polygenic predictors than were fluid measures. This mirrored heritability differences reported previously in adults and suggests similar associations in children. This may be consistent with a prominent role of gene-environment correlation in cognitive development measured by crystallized intelligence tests. Environmental and experiential mediators may represent malleable targets for improving cognitive outcomes.

It is important to both protect the healthy development and maintain the oral health of the child population. The study examined the effect of early childhood exposures to water fluoridation on measures of school-age executive functioning and emotional and behavioral development in a population-based sample. This longitudinal follow-up study used information from Australia's National Child Oral Health Study 2012-14. Children aged 5 to 10 y at baseline were contacted again after 7 to 8 y, before they had turned 18 y of age. Percent lifetime exposed to fluoridated water (%LEFW) from birth to the age 5 y was estimated from residential history and postcode-level fluoride levels in public tap water. Measures of children's emotional and behavioral development were assessed by the Strength and Difficulties Questionnaire (SDQ), and executive functioning was measured by the Behavior Rating Inventory of Executive Function (BRIEF). Multivariable regression models were generated to compare the associations between the exposure and the primary outcomes and controlled for covariates. An equivalence test was also conducted to compare the primary outcomes of those who had 100% LEFW against those with 0% LEFW. Sensitivity analysis was also conducted. A total of 2,682 children completed the SDQ and BRIEF, with mean scores of 7.0 (95% confidence interval, 6.6-7.4) and 45.3 (44.7-45.8), respectively. Those with lower %LEFW tended to have poorer scores of the SDQ and BRIEF. Multivariable regression models reported no association between exposure to fluoridated water and the SDQ and BRIEF scores. Low household income, identifying as Indigenous, and having a neurodevelopmental diagnosis were associated with poorer SDQ/BRIEF scores. An equivalence test confirmed that the SDQ/BRIEF scores among those with 100% LEFW were equivalent to that of those who had 0% LEFW. Exposure to fluoridated water during the first 5 y of life was not associated with altered measures of child emotional and behavioral development and executive functioning.

There is considerable debate about whether bilingual children have an advantage in executive functioning relative to monolingual children. In the current meta-analysis, we addressed this debate by comprehensively reviewing the available evidence. We synthesized data from published studies and unpublished data sets, which equated to 1,194 effect sizes from 10,937 bilingual and 12,477 monolingual participants between the ages of 3 and 17 years. Bilingual language status had a small overall effect on children's executive functioning ( g = .08, 95% confidence interval = [.01, .14]). However, the effect of language status on children's executive functioning was indistinguishable from zero ( g = -.04) after we adjusted for publication bias. Further, no significant effects were apparent within the executive-attention domain, in which the effects of language status have been hypothesized to be most pronounced ( g = .06, 95% confidence interval = [-.02, .14]). Taken together, available evidence suggests that the bilingual advantage in children's executive functioning is small, variable, and potentially not attributable to the effect of language status.

Retrospective self-report assessments of adults' childhood experiences with their parents are widely employed in psychological science, but such assessments are rarely validated against actual parenting experiences measured during childhood. Here, we leveraged prospectively acquired data characterizing mother-child and father-child relationship quality using observations, parent reports, and child reports covering infancy through adolescence. At age 26 years, approximately 800 participants completed a retrospective measure of maternal and paternal emotional availability during childhood. Retrospective reports of childhood emotional availability demonstrated weak convergence with composites reflecting prospectively acquired observations ( R 2 s = .01-.05) and parent reports ( R 2 s = .02-.05) of parenting quality. Retrospective parental availability was more strongly associated with prospective assessments of child-reported parenting quality ( R 2 s = .24-.25). However, potential sources of bias (i.e., depressive symptoms and family closeness and cohesiveness at age 26 years) accounted for more variance in retrospective reports (39%-40%) than did prospective measures (26%), suggesting caution when using retrospective reports of childhood caregiving quality as a proxy for prospective data.

After two strangers have briefly interacted with one another, both believe that they like their partner more than their partner likes them. A plausible explanation for this liking gap is that people are constantly worrying about how others are evaluating them. If so, one would expect the liking gap to emerge in young children as they become more concerned with their reputations and the impression they make on other people. The current study ( N = 241 U.S. children; age range = 4-11 years) supported this hypothesis, showing a liking gap beginning when children were 5 years old, the age at which they first become concerned with other people's evaluations of them. Moreover, the liking gap became more pronounced as children got older. These findings provide the first developmental description of the liking gap and support the hypothesis that this phenomenon is related to individuals' concerns for how others evaluate them.

In this preregistered field study, we examined preschool children's selective trust in a real-life situation. We investigated whether 3- to 6-year-old children (total N = 240) could be lured to a new location within their school grounds by an unfamiliar adult confederate. In a between-subjects manipulation, the confederate established either a high or a low level of personal credibility by providing information that the child knew to be either true or false. In Experiment 1, in which the confederate was female, children showed sensitivity to informational accuracy by being less willing to leave with an uninformed confederate, and this effect increased with age. In Experiment 2, in which the confederate was male, children were reluctant to leave regardless of informational accuracy. These findings point to real-world implications of epistemic-trust research and provide the first evidence regarding the early development of selective trust in a high-stakes naturalistic context.

Electronic-media use is associated with sleep disruptions in childhood and adolescence, although research relies primarily on subjective sleep. Effortful control, a dimension of self-regulation, may mitigate this association by helping children disengage from and regulate responses to media. We examined associations between media use and multiple actigraph-measured sleep parameters at mean and day levels and tested children's effortful control as a moderator of mean-level relations. We collected actigraph data and parents' diary reports of children's prebedtime television, video-game, laptop, desktop, cell-phone, and tablet use in 547 twin children (7-9 years old; 51.74% female). Mean-level media use was associated with bedtime and sleep duration. For the proportion of nights on which twins used media, but not the average number of media types, effortful control attenuated associations between media use and reduced sleep duration and efficiency. Day-level media use was related only to bedtime. Findings replicate and extend existing research and highlight self-regulation as a potential protective factor.

Observed genetic associations with educational attainment may be due to direct or indirect genetic influences. Recent work highlights genetic nurture , the potential effect of parents' genetics on their child's educational outcomes via rearing environments. To date, few mediating childhood environments have been tested. We used a large sample of genotyped mother-child dyads ( N = 2,077) to investigate whether genetic nurture occurs via the prenatal environment. We found that mothers with more education-related genes are generally healthier and more financially stable during pregnancy. Further, measured prenatal conditions explain up to one third of the associations between maternal genetics and children's academic and developmental outcomes at the ages of 4 to 7 years. By providing the first evidence of prenatal genetic nurture and showing that genetic nurture is detectable in early childhood, this study broadens our understanding of how parental genetics may influence children and illustrates the challenges of within-person interpretation of existing genetic associations.

Communion and agency are often described as core human values. In adults, these values predict gendered role preferences. Yet little work has examined the extent to which young boys and girls explicitly endorse communal and agentic values and whether early gender differences in values predict boys' and girls' different role expectations. In a sample of 411 children between the ages of 6 and 14 years, we found consistent gender differences in endorsement of communal and agentic values. Across this age range, boys endorsed communal values less and agentic values more than did girls. Moreover, gender differences in values partially accounted for boys' relatively lower family versus career orientation, predicting their orientation over and above gender identification and parent reports of children's gender expression. These findings suggest that gender differences in core values emerge surprisingly early in development and predict children's expectations well before they make decisions about adopting adult roles in their own families.

Prospective, longitudinal analyses revealed that over a 12-year period from ages 6 to 18, individuals who grew up with mothers with more proenvironmental attitudes engaged in more proenvironmental behavior as young adults. A similar marginal association was uncovered between mothers' proenvironmental behaviors and the proenvironmental behavior of their young adult offspring. Maternal educational attainment, but not political ideology, was also associated with more proenvironmental behavior as children matured. Moreover, childhood time spent outdoors was positively associated with increased environmentally responsible behavior in young adulthood. Interestingly, one's own childhood proenvironmental behavior and attitude, at least as assessed at age 6, bear little on one's eventual proenvironmental behavior as a young adult. Finally, among this set of childhood factors, maternal education and childhood time spent outdoors were independent predictors of positive changes in environmental behavior from early childhood to young adulthood.

Positive attitude is thought to impact academic achievement and learning in children, but little is known about its underlying neurocognitive mechanisms. Using a large behavioral sample of 240 children, we found that positive attitude toward math uniquely predicted math achievement, even after we accounted for multiple other cognitive-affective factors. We then investigated the neural mechanisms underlying the link between positive attitude and academic achievement in two independent cohorts of children (discovery cohort: n = 47; replication cohort: n = 28) and tested competing hypotheses regarding the differential roles of affective-motivational and learning-memory systems. In both cohorts, we found that positive attitude was associated with increased engagement of the hippocampal learning-memory system. Structural equation modeling further revealed that, in both cohorts, increased hippocampal activity and more frequent use of efficient memory-based strategies mediated the relation between positive attitude and higher math achievement. Our study is the first to elucidate the neurocognitive mechanisms by which positive attitude influences learning and academic achievement.

We investigated whether young children were more likely to spontaneously attribute mental states to members of their own social group than to members of an out-group. We asked 5- and 6-year-old children to describe the actions of interacting geometric shapes and manipulated whether the children believed these shapes represented their own group or another group. Children of both ages spontaneously used mental-state words more often in their description of in-group members compared with out-group members. Furthermore, 6-year-olds produced a greater diversity of mental-state terms when talking about their own social group. These effects held across two different social categories (based on gender and geographic location). This research has important implications for understanding a broad range of social phenomena, including dehumanization, intergroup bias, and theory of mind.

Sometimes it is easy to do the right thing. But often, people act morally only after overcoming competing immoral desires. How does learning about someone's inner moral conflict influence children's and adults' moral judgments about that person? Across four studies, we discovered a striking developmental difference: When the outcome is held constant, 3- to 8-year-old children judge someone who does the right thing without experiencing immoral desires to be morally superior to someone who does the right thing through overcoming conflicting desires-but adults have the opposite intuition. This developmental difference also occurs for judgments of immoral actors: Three- to 5-year-olds again prefer the person who is not conflicted, whereas older children and adults judge that someone who struggles with the decision is morally superior. Our findings suggest that children may begin with the view that inner moral conflict is inherently negative, but, with development, come to value the exercise of willpower and self-control., (© The Author(s) 2016.)

Many significant changes occur during human childhood, including cognitive, social-cognitive, and socioemotional changes. This article reviews some key phenomena associated with some of these changes and attempts to capture them within a single conceptual umbrella-changes in children's shared realities with others Shared reality is the experience that you have an inner state about something (e.g., a feeling or belief or concern about something) that is shared by others (a person or group). Four phases of shared-reality development are proposed: Phase 1 (6-12 months) shared feelings; Phase 2 (18-24 months) shared practices; Phase 3 (3-5 years) shared self-guides; Phase 4 (9-13 years) shared coordinated roles In each phase, a new way that children interact with and relate to others emerges, and the emergence of each new shared-reality mode has significant self-regulatory and social consequences. These consequences include both major benefits for children and potential costs-trade-offs of being human., (© The Author(s) 2016.)

Children's intelligence mind-sets (i.e., their beliefs about whether intelligence is fixed or malleable) robustly influence their motivation and learning. Yet, surprisingly, research has not linked parents' intelligence mind-sets to their children's. We tested the hypothesis that a different belief of parents-their failure mind-sets-may be more visible to children and therefore more prominent in shaping their beliefs. In Study 1, we found that parents can view failure as debilitating or enhancing, and that these failure mind-sets predict parenting practices and, in turn, children's intelligence mind-sets. Study 2 probed more deeply into how parents display failure mind-sets. In Study 3a, we found that children can indeed accurately perceive their parents' failure mind-sets but not their parents' intelligence mind-sets. Study 3b showed that children's perceptions of their parents' failure mind-sets also predicted their own intelligence mind-sets. Finally, Study 4 showed a causal effect of parents' failure mind-sets on their responses to their children's hypothetical failure. Overall, parents who see failure as debilitating focus on their children's performance and ability rather than on their children's learning, and their children, in turn, tend to believe that intelligence is fixed rather than malleable., (© The Author(s) 2016.)

Although attention-deficit/hyperactivity disorder (ADHD) is a heritable neurodevelopmental condition, there is also considerable scientific and public interest in environmental modulators of its etiology. Exposure to neurotoxins is one potential source of perturbation of neural, and hence psychological, development. Exposure to lead in particular has been widely investigated and is correlated with neurodevelopmental outcomes, including ADHD. To investigate whether this effect is likely to be causal, we used a Mendelian randomization design with a functional gene variant. In a case-control study, we examined the association between ADHD symptoms in children and blood lead level as moderated by variants in the hemochromatosis (HFE) gene. The HFE gene regulates iron uptake and secondarily modulates lead metabolism. Statistical moderation was observed: The magnitude of the association of blood lead with symptoms of ADHD was altered by functional HFE genotype, which is consistent with a causal hypothesis., (© The Author(s) 2015.)

Socioemotional risks associated with nonparental care have been debated for decades, and research findings continue to be mixed. Yet few studies have been able to test the causal hypothesis that earlier, more extensive, and longer durations of nonmaternal care lead to more problems. To examine the consequences of age of entry into nonparental care for childhood aggression, we used prospective longitudinal data from Norway, where month of birth partly determines age of entry into Early Childhood Education and Care (ECEC) centers. In this sample of 939 children followed from ages 6 months through 4 years, ECEC teachers reported the children's aggression when they were 2, 3, and 4 years old. We found some evidence that age of entry into ECEC predicted aggression at age 2, albeit modestly and not robustly. Between the ages of 2 and 4 years, the effect of age of entry on aggression faded to negligible levels. The implications for psychological science and policy are discussed., (© The Author(s) 2015.)

In this study, we drew on prospective, longitudinal data to investigate the long-term predictive significance of the quality of early parent-child relationship experiences for adults' sympathetic nervous system (SNS) activity during conflict discussions with their romantic partners. Maternal sensitivity was repeatedly assessed across childhood via direct observations of mother-child interactions. When the children in the study became adults (34-37 years old), electrodermal activity-an index of SNS arousal and a psychophysiological marker of behavioral inhibition-was recorded for 37 participants while at rest and while they attempted to resolve conflicts in their romantic relationships. Individuals who had experienced less sensitive maternal caregiving during childhood had greater increases in electrodermal activity during conflict discussions with their adult partners, relative to resting conditions. This longitudinal association was not accounted for by observed or self-reported romantic-relationship quality, gender, ethnicity, or early socioeconomic factors., (© The Author(s) 2015.)

This study examined whether variations in brain development between kindergarten and Grade 3 predicted individual differences in reading ability at Grade 3. Structural MRI measurements indicated that increases in the volume of two left temporo-parietal white matter clusters are unique predictors of reading outcomes above and beyond family history, socioeconomic status, and cognitive and preliteracy measures at baseline. Using diffusion MRI, we identified the left arcuate fasciculus and superior corona radiata as key fibers within the two clusters. Bias-free regression analyses using regions of interest from prior literature revealed that volume changes in temporo-parietal white matter, together with preliteracy measures, predicted 56% of the variance in reading outcomes. Our findings demonstrate the important contribution of developmental differences in areas of left dorsal white matter, often implicated in phonological processing, as a sensitive early biomarker for later reading abilities, and by extension, reading difficulties., (© The Author(s) 2014.)

Although one third of children and adolescents are overweight or obese, developmental changes in food craving and the ability to regulate craving remain poorly understood. We addressed this knowledge gap by examining behavioral and neural responses to images of appetizing unhealthy foods in individuals ages 6 through 23 years. On close trials (assessing unregulated craving), participants focused on a pictured food's appetitive features. On far trials (assessing effortful regulation), participants focused on a food's visual features and imagined that it was farther away. Across conditions, older age predicted less craving, less striatal recruitment, greater prefrontal activity, and stronger frontostriatal coupling. When effortfully regulating their responses to the images, all participants reported less craving and exhibited greater recruitment of lateral prefrontal cortex and less recruitment of ventromedial prefrontal cortex. Greater body mass predicted less regulation-related prefrontal activity, particularly among children. These results suggest that children experience stronger craving than adults but can also effectively regulate craving. Moreover, the mechanisms underlying regulation may differ for heavy and lean children., (© The Author(s) 2014.)

There has been a push in recent years for students with disabilities to be educated alongside their typically developing peers, a practice called inclusion. In this study, we sought to determine whether peer effects operate within early-childhood special-education (ECSE) classrooms in which preschoolers with disabilities are educated alongside typical peers. Peer effects specific to language growth were assessed for 670 preschoolers (mean age = 52 months) in 83 ECSE classrooms; 55% of the children had disabilities. We found that the average language skills of classmates, as assessed in the fall of the year, significantly predicted children's language skills in the spring (after controlling for their relative skill level in the fall); in addition, there was a significant interactive effect of disability status (i.e., the presence or absence of a disability) and peers' language skills. Peer effects were the least consequential for children without disabilities whose classmates had relatively strong language skills, and the most consequential for children with disabilities whose classmates had relatively poor language skills., (© The Author(s) 2014.)

Metacognition, the ability to assess one's own knowledge, has been targeted as a critical learning mechanism in mathematics education. Yet the early childhood origins of metacognition have proven difficult to study. Using a novel nonverbal task and a comprehensive set of metacognitive measures, we provided the strongest evidence to date that young children are metacognitive. We showed that children as young as 5 years made metacognitive "bets" on their numerical discriminations in a wagering task. However, contrary to previous reports from adults, our results showed that children's metacognition is domain specific: Their metacognition in the numerical domain was unrelated to their metacognition in another domain (emotion discrimination). Moreover, children's metacognitive ability in only the numerical domain predicted their school-based mathematics knowledge. The data provide novel evidence that metacognition is a fundamental, domain-dependent cognitive ability in children. The findings have implications for theories of uncertainty and reveal new avenues for training metacognition in children., (© The Author(s) 2014.)

This study examined whether, as mothers' depressive symptoms increase, their expressions of negative emotion to children increasingly reflect aversion sensitivity and motivation to minimize ongoing stress or discomfort. In multiple interactions over 2 years, negative affect expressed by 319 mothers and their children was observed across variations in mothers' depressive symptoms, the aversiveness of children's immediate behavior, and observed differences in children's general negative reactivity. As expected, depressive symptoms predicted reduced maternal negative reactivity when child behavior was low in aversiveness, particularly with children who were high in negative reactivity. Depressive symptoms predicted high negative reactivity and steep increases in negative reactivity as the aversiveness of child behavior increased, particularly when high and continued aversiveness from the child was expected (i.e., children were high in negative reactivity). The findings are consistent with the proposal that deficits in parenting competence as depressive symptoms increase reflect aversion sensitivity and motivation to avoid conflict and suppress children's aversive behavior., (© The Author(s) 2014.)

In the research reported here, we examined whether individual differences in authoritarianism have expressions in early childhood. We expected that young children would be more responsive to cues of deviance and status to the extent that their parents endorsed authoritarian values. Using a sample of 43 preschoolers and their parents, we found support for both expectations. Children of parents high in authoritarianism trusted adults who adhered to convention (vs. adults who did not) more than did children of parents low in authoritarianism. Furthermore, compared with children of parents low in authoritarianism, children of parents high in authoritarianism gave greater weight to a status-based "adult = reliable" heuristic in trusting an ambiguously conventional adult. Findings were consistent using two different measures of parents' authoritarian values. These findings demonstrate that children's trust-related behaviors vary reliably with their parents' orientations toward authority and convention, and suggest that individual differences in authoritarianism express themselves well before early adulthood.

Humans demonstrate a clear bias toward members of their own group over members of other groups in a variety of ways. It has been argued that the motivation underlying this in-group bias in adults may be favoritism toward one's own group (in-group love), derogation of the out-group (out-group hate), or both. Although some studies have demonstrated in-group bias among children and infants, nothing is known about the underlying motivations of this bias. Using a novel game, we found that in-group love is already present in children of preschool age and can motivate in-group-biased behavior across childhood. In contrast, out-group hate develops only after a child's sixth birthday and is a sufficient motivation for in-group-biased behavior from school age onward. These results help to better identify the motivation that underlies in-group-biased behavior in children.

Adaptation by natural selection is a core mechanism of evolution. It is also one of the most widely misunderstood scientific processes. Misconceptions are rooted in cognitive biases found in preschoolers, yet concerns about complexity mean that adaptation by natural selection is generally not comprehensively taught until adolescence. This is long after untutored theoretical misunderstandings are likely to have become entrenched. In a novel approach, we explored 5- to 8-year-olds' capacities to learn a basic but theoretically coherent mechanistic explanation of adaptation through a custom storybook intervention. Experiment 1 showed that children understood the population-based logic of natural selection and also generalized it. Furthermore, learning endured 3 months later. Experiment 2 replicated these results and showed that children understood and applied an even more nuanced mechanistic causal explanation. The findings demonstrate that, contrary to conventional educational wisdom, basic natural selection is teachable in early childhood. Theory-driven interventions using picture storybooks with rich explanatory structure are beneficial.

In current Western society, children are often lavished with inflated praise (e.g., "You made an incredibly beautiful drawing!"). Inflated praise is often given in an attempt to raise children's self-esteem. An experiment (Study 1) and naturalistic study (Study 2) found that adults are especially inclined to give inflated praise to children with low self-esteem. This inclination may backfire, however. Inflated praise might convey to children that they should continue to meet very high standards-a message that might discourage children with low self-esteem from taking on challenges. Another experiment (Study 3) found that inflated praise decreases challenge seeking in children with low self-esteem and has the opposite effect on children with high self-esteem. These findings show that inflated praise, although well intended, may cause children with low self-esteem to avoid crucial learning experiences.

Cognitive skills predict academic performance, so schools that improve academic performance might also improve cognitive skills. To investigate the impact schools have on both academic performance and cognitive skills, we related standardized achievement-test scores to measures of cognitive skills in a large sample (N = 1,367) of eighth-grade students attending traditional, exam, and charter public schools. Test scores and gains in test scores over time correlated with measures of cognitive skills. Despite wide variation in test scores across schools, differences in cognitive skills across schools were negligible after we controlled for fourth-grade test scores. Random offers of enrollment to oversubscribed charter schools resulted in positive impacts of such school attendance on math achievement but had no impact on cognitive skills. These findings suggest that schools that improve standardized achievement-test scores do so primarily through channels other than improving cognitive skills.

In the study reported here, the main question we investigated was whether attention style could be a conditional adaptation. We organized participants of the TRacking Adolescents' Individual Lives Survey (TRAILS; N = 2,230) into shifters, sustainers, and two comparison groups, depending on their performance on a shifting- and a sustained-attention task at age 11 years. Compared with sustainers, shifters reported more pre- and perinatal risk factors and more childhood stress, and they adopted a faster life-history strategy. These differences were not found between the comparison groups, who performed well or poorly on both tasks, which suggests that specialization for either sustained or shifting attention is the key to conditional adaptation. In a subsample (n = 860), we found that stress did not increase depression risk in shifters, whereas a mismatch between early and recent stress predicted depression in sustainers. Cumulative stress predicted depression in the comparison group. These results suggest that shifters retain high levels of plasticity throughout life, whereas sustainers' adapted their phenotype early in life to the expected mature environment.

In suggesting that new nations often coalesce in the decades following war, historians have posed an important psychological question: Does the experience of war generate an enduring elevation in people's egalitarian motivations toward their in-group? We administered social-choice tasks to more than 1,000 children and adults differentially affected by wars in the Republic of Georgia and Sierra Leone. We found that greater exposure to war created a lasting increase in people's egalitarian motivations toward their in-group, but not their out-groups, during a developmental window starting in middle childhood (around 7 years of age) and ending in early adulthood (around 20 years of age). Outside this window, war had no measurable impact on social motivations in young children and had only muted effects on the motivations of older adults. These "war effects" are broadly consistent with predictions from evolutionary approaches that emphasize the importance of group cooperation in defending against external threats, though they also highlight key areas in need of greater theoretical development.

Genes account for increasing proportions of variation in cognitive ability across development, but the mechanisms underlying these increases remain unclear. We conducted a meta-analysis of longitudinal behavioral genetic studies spanning infancy to adolescence. We identified relevant data from 16 articles with 11 unique samples containing a total of 11,500 twin and sibling pairs who were all reared together and measured at least twice between the ages of 6 months and 18 years. Longitudinal behavioral genetic models were used to estimate the extent to which early genetic influences on cognition were amplified over time and the extent to which innovative genetic influences arose with time. Results indicated that in early childhood, innovative genetic influences predominate but that innovation quickly diminishes, and amplified influences account for increasing heritability following age 8 years.

Using a longitudinal cluster-randomized controlled design, we examined whether students' reading outcomes differed when they received 1, 2, or 3 years of individualized reading instruction from first through third grade, compared with a treated control group. More than 45% of students came from families living in poverty. Following students, we randomly assigned their teachers each year to deliver individualized reading instruction or a treated control condition intervention focused on mathematics. Students who received individualized reading instruction in all three grades showed the strongest reading skills by the end of third grade compared with those who received fewer years of such instruction. There was inconsistent evidence supporting a sustained first-grade treatment effect: Individualized instruction in first grade was necessary but not sufficient for stronger third-grade reading outcomes. These effects were achieved by regular classroom teachers who received professional development, which indicates that policies that support the use of evidence-based reading instruction and teacher training can yield increased student achievement.