School readiness among vulnerable children: a systematic review of studies using a person-centered approach.

BACKGROUND: Research has consistently shown that some children are more vulnerable at the time of school readiness. Better understanding the characteristics of these children is therefore important. Most studies have used a variable-based approach, which may mask the presence of small but important subgroups of children with mixed patterns of readiness strengths and weaknesses. Identifying subgroups with mixed readiness patterns using a person-centered approach matters because their developmental trajectories might differ in important ways from children with broader difficulties across all readiness domains. OBJECTIVE: This systematic review attempts to synthesize existing profiles of school readiness conducted on preschool-aged children and to describe how these various profiles are associated with children's academic achievement and social adjustment during their school years. Specifically, we described how the school readiness profiles vary in number of profiles identified and differences in the specific domains of school readiness. We further describe the school readiness profiles and how they predict later academic and social outcomes. Furthermore, we focus on profile differences between at-risk and non-at-risk preschoolers. METHODS: Longitudinal studies published between 2005 and 2022 on profiles of school readiness before school entry and at least one subsequent academic and/or social outcomes were extracted from five databases. Eight articles were included in this systematic review out of the 117 screened peer-reviewed articles. RESULTS: All the studies incorporated both the cognitive and socioemotional domains of school readiness in their profiles. Fifteen profiles of school readiness at preschool age were identified based on the child level of cognitive and socioemotional skills, with 7 profiles at risk of later academic and social difficulties. Despite variation, children in these at-risk profiles of school readiness shared similar features. CONCLUSION: This literature review provides an exhaustive summary on the number of profiles and domains of school readiness most frequently reported in studies using a person-centered approach. Yielding an in-depth description of at-risk profiles of school readiness can help designing early preventive intervention for these children.

Preschooler Screen Time During the Pandemic Is Prospectively Associated With Lower Achievement of Developmental Milestones.

OBJECTIVE: The aim of this study was to assess the developmental risks associated with total screen time, and specifically newer mobile devices, in the context of the pandemic. METHODS: This study uses parent-reported data from a prospective cohort of Canadian preschool-age children. The exposure variable is child daily screen time measured at the age of 3.5 years categorized as light (<1 hr/d), moderate (1-4 hr/d), or intensive (>4 hr/d) use (N = 315). Time spent on mobile devices was considered separately as a continuous variable. Our outcome is child global development scores, which combine assessments of communication, cognitive, personal-social, and motor skills measured at the age of 4.5 years using the Ages and Stages Questionnaire (ASQ) (N = 249, 79% retained). ASQ scores were dichotomized to distinguish children at risk of developmental delays (below the 15th percentile) from those not at risk. We estimate associations between child screen time and later global development using multiple regressions adjusted for child sex and temperament, and parent education. We also examine whether associations are moderated by child and parent characteristics. RESULTS: Logistic regressions revealed that intensive users were more at risk of global developmental delays compared with light users (OR = 4.29, p = 0.020). Mobile device use was also associated with lower global scores (ß = -3.064; p = 0.028), but not with risk of delays. We found no evidence that associations were moderated by child sex and temperament, or parent education. CONCLUSION: The findings suggest that intensive screen time may be associated with delays in child global development. Early childhood professionals should encourage families with preschoolers to prioritize screen-free activities to promote optimal cognitive, language, social, and motor development.

Partners with a Highly Favorable Attitude Toward Breastfeeding Contribute to Promoting Initiation and Length of Breastfeeding for More than 5 Months in a Population-Based Canadian Study.

Introduction: Promoting maternal breastfeeding for at least 6 months is important to improve children physical health during infancy and neurodevelopmental outcomes in childhood. For this guideline to be followed, it is paramount to identify what factors best support the initiation and length of breastfeeding. This study estimates the contribution of various child- and parent-level factors, as well as the sociodemographic context in predicting maternal breastfeeding initiation and duration. Methods: This study draws on data from the Quebec Longitudinal Study of Child Development. Mothers who never breastfed when the infant was 5 months old (n = 630, 28.3%) were compared to mothers who breastfed for less than 5 months (n = 844, 38.0%) and mothers breastfeeding for more than 5 months (n = 749, 33.7%), using multivariable multinomial regression models. Results: Mothers with a partner showing a positive attitude toward breastfeeding were up to 13 times more likely to breastfeed their infant for more than 5 months. The positive attitude of partners toward breastfeeding was the strongest predictor of breastfeeding duration, followed by the maternal educational attainment and timing she returns to work. Most prenatal and perinatal child-level factors and the sociodemographic context predicted breastfeeding duration, but to a lesser extent. Discussion: This finding underscores the role of the partner's attitude in promoting initiation and length of breastfeeding. As such, educational campaigns and health practitioners could target both the mother and their partner in promoting breastfeeding.

School readiness among vulnerable children: a systematic review of studies using a person-centered approach

Abstract Background Research has consistently shown that some children are more vulnerable at the time of school readiness. Better understanding the characteristics of these children is therefore important. Most studies have used a variable-based approach, which may mask the presence of small but important subgroups of children with mixed patterns of readiness strengths and weaknesses. Identifying subgroups with mixed readiness patterns using a person-centered approach matters because their developmental trajectories might differ in important ways from children with broader difficulties across all readiness domains. Objective This systematic review attempts to synthesize existing profiles of school readiness conducted on preschool-aged children and to describe how these various profiles are associated with children's academic achievement and social adjustment during their school years. Specifically, we described how the school readiness profiles vary in number of profiles identified and differences in the specific domains of school readiness. We further describe the school readiness profiles and how they predict later academic and social outcomes. Furthermore, we focus on profile differences between at-risk and non-at-risk preschoolers. Methods Longitudinal studies published between 2005 and 2022 on profiles of school readiness before school entry and at least one subsequent academic and/or social outcomes were extracted from five databases. Eight articles were included in this systematic review out of the 117 screened peer-reviewed articles. Results All the studies incorporated both the cognitive and socioemotional domains of school readiness in their profiles. Fifteen profiles of school readiness at preschool age were identified based on the child level of cognitive and socioemotional skills, with 7 profiles at risk of later academic and social difficulties. Despite variation, children in these at-risk profiles of school readiness shared similar features. Conclusion This literature review provides an exhaustive summary on the number of profiles and domains of school readiness most frequently reported in studies using a person-centered approach. Yielding an in-depth description of at-risk profiles of school readiness can help designing early preventive intervention for these children.

Unraveling the effects of maternal breastfeeding duration and exclusive breast milk on children's cognitive abilities in early childhood.

Background: This study investigated the putative associations between mothers' use of exclusive breast milk and the duration of breastfeeding with child cognitive development. Methods: This study is based on 2,210 Canadian families with children assessed longitudinally from age 4 to 7 years on their memory-span and math skills. These cognitive abilities were measured with standardized tasks. Breastfeeding practices were collected via maternal reports. We applied propensity scores to control the social selection bias for breastfeeding. Results: Results adjusted for propensity scores and sample weight revealed no significant differences between non-breastfed children with those being non-exclusively breastfed for 5 months or less, and with children being exclusively breastfed for 9.2 months on average, on their early math skills and memory-span. We found that children who were non-exclusively breastfed for 6.8 months on average had a slightly higher levels of memory-span at age 4 than children who were never breastfed, and this small but significant difference lasted up to age 7. Conclusion: Our findings suggest no significant differences between children being exclusively breastfed and those fed with formula on their early math skills and memory-span. The encouragement of breastfeeding to promote child cognitive school readiness may, in some case (non-exclusive breastfeeding for more than 5 months), show a small but long-lasting advantage in early memory-span.

Meeting preschool screen time recommendations: which parental strategies matter?

Background: High levels of screen use by preschoolers may contribute to adverse health and developmental outcomes. Little is known about which parental strategies may be protective against intensive screen use by children. Our aim is to estimate whether parent strategies for mediating child screen time including restrictive and instructive mediation and social coviewing, predict preschooler adherence to the screen time recommendation of ≤1 h/day during the COVID-19 pandemic. We also examine if parent restrictive mediation interacts with child temperament characteristics. Methods: Our sample is composed of 315 Canadian parents of preschoolers surveyed during the COVID-19 pandemic. Parents provided measures of child adherence to screen time guidelines at ages 3.5 (baseline) and 4.5 years. Parents also reported how often they used restrictive and instructional mediation, and social coviewing to manage their child's screen use. Control variables include child sex and temperament (effortful control, negative affectivity, extraversion), educational attainment, and parenting stress at age 3.5. Results: A logistic regression revealed that parental restrictiveness was associated with a 4 time increase in the odds of adherence to screen time guidelines, OR = 4.07 (95% CI [1.70-13.03]). Parental social coviewing decreased the chances of adherence by 80% (OR = 0.20, 95% CI [0.09-0.48]). Furthermore, children not meeting recommendation at 3.5 were 98% less likely to respect the recommendation 1 year later (OR = 0.02, 95% CI [0.01-0.07]). Results were adjusted for child sex, temperament, baseline screen time, and parent education and stress The interaction between the restriction mediation and child temperament on later screen time was not significant. Conclusion: Our results indicate that some parental strategies may be more effective than others for managing preschooler screen time. Parent use of restrictive mediation was most likely to forecast child adherence to later screen time recommendations. The present results may contribute to the development of targeted family-based interventions designed to promote healthy development from a young age.

Adolescent internet use predicts higher levels of generalized and social anxiety symptoms for girls but not boys.

Past research suggests that internet use can increase the risks of internalizing symptoms in adolescents. However, bidirectional relationships between adolescent internet use and anxiety symptoms have received very little attention. Furthermore, few studies have examined these links according to sex. The present study attempts to fill this gap by investigating longitudinal associations between Canadian boys' and girls' internet use and symptoms of generalized anxiety and social anxiety using data from the Quebec longitudinal Study of Child Development. A sample of 1324 adolescents (698 girls, 626 boys) self-reported the number of hours per week they spent on the internet and their symptoms of generalized and social anxiety at ages 15 and 17. We estimated two cross-lagged panel models with social or generalized anxiety symptoms and internet use at age 15 predicting those same variables at age 17. Sex was used as a grouping variable and socioeconomic status was included as a control variable. Internet use at 15 predicted generalized and social anxiety symptoms at age 17 in girls, but not boys. Social and generalized anxiety symptoms at age 15 did not predict internet use at age 17 for both boys and girls. These results suggest that internet use can be a significant risk factor for the development of anxiety symptoms in adolescent girls. Girls may be more vulnerable to the negative effects of internet use due to increased sensitivity to social comparisons. Thus, helping girls develop healthier internet use habits should be a target for promoting their mental health.

Maternal Labor Force Participation During the Child's First Year and Later Separation Anxiety Symptoms.

Separation anxiety symptoms are frequent among preschool-aged children, but it is also a possible gateway for diagnosis of separation anxiety disorder. Early maternal employment after childbirth can increase the risk for the development of separation anxiety symptoms. From an economic perspective, however, securing employment is one effective strategy to ensure child well-being. This study investigated how mothers' participation in the labor force (vs. maternal leave) and the financial state of families when the child was 5 months old was prospectively associated with separation anxiety symptoms. This study is based on 1,295 Canadian families with children assessed longitudinally from 17 months to age 6 on their levels of separation anxiety. Separation anxiety was measured during face-to-face interviews with the mothers. Maternal labor force participation, financial status, and risk factors were measured at 5 months. Results adjusted for propensity scores and for sample weight revealed that children of working mothers, despite having sufficient income (n = 245, 18.9%), were at higher risk of separation anxiety during early childhood. In contrast, maternity leave was most beneficial for children's separation anxiety, whether they were in a family with sufficient income (n = 950, 73.4%) or temporary low income (n = 100, 7.7%). Children of mothers in maternity leave were at risk of heightened separation anxiety only if they experienced chronic economic hardship. Therefore, maternity leave uptake could help prevent the development of separation anxiety. Providing families with opportunity to care for the baby as their main occupation during this sensitive developmental period could help improve children's mental health.

Prospective associations between child screen time and parenting stress and later inattention symptoms in preschoolers during the COVID-19 pandemic.

Introduction: Child attention skills are critical for supporting self-regulation abilities, especially during the first years of life. On the other hand, inattention symptoms in preschoolers have been associated with poor school readiness, literacy skills and academic achievement. Previous research has linked excessive screen time with increased inattention symptoms in early childhood. However, most research has only focused on TV exposure and did not investigate this association during the COVID-19 pandemic. This atypical context has increased screen time in children worldwide, including preschoolers. We hypothesize that higher levels of child screen media and parenting stress at age 3.5 will be associated with higher child inattention symptoms at age 4.5. Method: This study draws on participants followed longitudinally over the span of 2-years for an investigation of Canadian preschoolers' screen media use during the pandemic (N = 315, 2020). A follow-up with this sample was completed in 2021 (N = 264). Results: Analyses using multiple linear regression, revealed a positive association between child screen time at age 3.5 and inattention symptoms at 4.5 years. Parental stress was also positively associated with child inattention symptoms. Associations were observed above individual (child age, inhibitory control, and sex) and family (parent education and family income) characteristics. Discussion: These results confirmed our hypothesis and highlight that preschooler screen use and parenting stress may undermine attentional skills. Since attention is a crucial component for children development, behavior and academic outcomes, our study reinforces the importance for parents of adopting healthy media habits.

Adolescent anxiety and pain problems: A joint, genome-wide investigation and pathway-based analysis.

Both common pain and anxiety problems are widespread, debilitating and often begin in childhood-adolescence. Twin studies indicate that this co-occurrence is likely due to shared elements of risk, rather than reciprocal causation. A joint genome-wide investigation and pathway/network-based analysis of adolescent anxiety and pain problems can identify genetic pathways that subserve shared etiopathogenetic mechanisms. Pathway-based analyses were performed in the independent samples of: The Quebec Newborn Twin Study (QNTS; 246 twin pairs and 321 parents), the Longitudinal Study of Child Development in Quebec (QLSCD; n = 754), and in the combined QNTS and QLSCD sample. Multiple suggestive associations (p<1×10-5), and several enriched pathways were found after FDR correction for both phenotypes in the QNTS; many nominally-significant enriched pathways overlapped between pain problems and anxiety symptoms (uncorrected p<0.05) and yielded results consistent with previous studies of pain or anxiety. The QLSCD and the combined QNTS and QLSCD sample yielded similar findings. We replicated an association between the pathway involved in the regulation of myotube differentiation (GO:0010830) and both pain and anxiety problems in the QLSDC and the combined QNTS and QLSCD sample. Although limited by sample size and thus power, these data provide an initial support to conjoint molecular investigations of adolescent pain and anxiety problems. Understanding the etiology underlying pain and anxiety co-occurrence in this age range is relevant to address the nature of comorbidity and its developmental pathways, and shape intervention. The replication across samples implies that these effects are reliable and possess external validity.

Preschooler screen time and temperamental anger/frustration during the COVID-19 pandemic.

BACKGROUND: In the context of increased media use and family distress during the pandemic, we examine whether preschooler screen time at age 3.5 contributes to later expressions of anger/frustration at 4.5, while also considering the inverse association. METHODS: Data are from a cohort of 315 Canadian preschool-aged children during the COVID-19 pandemic. Parent-reported measures included child h/day of screen time and child temperamental anger/frustration, both measured at 3.5 and 4.5 years of age. Indicators of family distress include use of childcare and child sleep, family income, parenting stress, and parent education, marital and employment status. We also consider child sex as a control variable. RESULTS: A crossed-lagged panel model revealed continuity in screen time between the ages of 3.5 and 4.5 (ß = 0.68) and temperamental anger/frustration from 3.5 to 4.5 (ß = 0.60). Child screen time at age 3.5 predicted increased proneness to anger/frustration at age 4.5 (ß = 0.14). Anger/frustration at age 3.5 did not predict screen time at age 4.5. CONCLUSION: Our results suggest that preschooler screen time during the pandemic may have undermined the ability to regulate negative emotions, a key component of social and academic competence. Supporting parents in implementing healthy media habits post pandemic may benefit young children's development. IMPACT: Key message: this study observes prospective bidirectional associations between preschoolers screen time and temperamental displays of anger or frustration during the COVID-19 pandemic. What does it add: we provide evidence that preschool screen time at age 3.5 prospectively contributes to the tendency to react in anger/frustration at age 4.5. In contrast, greater proneness to anger/frustration did not predict later exposure to screen time. What is the impact: health practitioners should enquire about media use habits during well-child visits to foster children's healthy development during the preschool years.

Classroom Placement and Twins' Social Behaviors in Elementary School: Providing Empirical Evidence to Inform Educational Policy.

Classroom placement of twins is an ongoing issue for educational policy. Many educational jurisdictions have standard policy most commonly founded in the belief that separation supports individual identity, personal development and academic opportunity. This study examined the effects of classroom placement in a sample of 560 twin pairs whose behaviors were assessed from ages 5 to 12 years. We found no detrimental effect of classroom sharing on twins' social development. In contrast, this study provides evidence that educating twins together is associated with modest positive twins' behaviors and social functioning at school. Implications for educational policies are further discussed.

Is the Association Between Early Childhood Screen Media Use and Effortful Control Bidirectional? A Prospective Study During the COVID-19 Pandemic.

Individual differences in effortful control, a component of temperament, reflecting the ability to use attention and other cognitive processes to self-regulate emotion and behavior, contribute to child academic adjustment, social competence, and wellbeing. Research has linked excessive screen time in early childhood to reduced self-regulation ability. Furthermore, research suggests that parents are more likely to use screens with children who have more challenging temperaments, such as low levels of effortful control. Since screen time by children between the ages of 0 and 18 has increased during the COVID-19 pandemic, it remains timely to investigate the developmental pattern of association between child screen media use and effortful control. We hypothesize that higher levels of screen media intake at age 3.5 will be associated with lower effortful control at age 4.5 and that lower effortful control at 3.5 will contribute to more screen media intake at age 4.5. This study draws on participants followed longitudinally over the span of 2-years for an investigation of Canadian preschoolers' screen media use during the pandemic (N = 316, Wave 1). A follow-up with this sample was completed in 2021 (N = 265, Wave 2). Analyses using a cross-lagged panel model revealed stability in child screen time and effortful control between the ages of 3.5 and 4.5. Child screen time at age 3.5 significantly contributed to decreased effortful control scores at the age of 4.5, whereas effortful control at age 3.5 did not contribute to screen time at age 4.5. Our results partially confirmed our hypothesis and indicated that higher levels of screen time intake were detrimental to the development of effortful control. These results suggest that screen media use, an exceedingly frequent activity, may play an enduring role in development by shaping young children's temperaments.

Maternal Functioning and Child's Externalizing Problems: Temperament and Sex-Based Driven Effects.

This study examines how maternal adverse parenting (hostility, neglect, low warmth) and psychological distress explain the associations between child temperament factors and externalizing problems. It also examines if these associations differ according to the child's biological sex. The sample consists of 339 school-age children receiving in-school services for conduct problems. Data were collected through questionnaires completed by mothers at 3 time points, at one-year intervals. Results from path analyses revealed that maternal psychological distress partly explained the associations between each child temperamental factors (negative affectivity, surgency/extraversion, effortful control) and levels of externalizing problems. Specifically, the indirect effect of psychological distress between child negative affectivity and externalizing problems was only significant for boys, not girls. Maternal hostility, on the other hand, mediated the association between child surgency/extraversion and externalizing problems in both boys and girls. Interestingly, neglectful parenting and maternal warmth did not explain the association between child temperamental factors and externalizing problems. The findings suggest small but significant temperament child-driven effects on maternal psychological distress and hostility, in turn, translating into higher levels of externalizing problems. These findings support the relevance of temperament-based interventions for children with conduct problems and of increased mental health support for their mothers. By aiding mothers in developing a larger repertoire of parenting strategies, mothers may be better equipped to respond appropriately to their child's various temperamental characteristics, hence, reducing their psychological distress and hostile behaviors and limiting the development of child externalizing problems.

Adolescent pain: appraisal of the construct and trajectory prediction-by-symptom between age 12 and 17 years in a Canadian twin birth cohort.

ABSTRACT: Adolescent pain is common and continues into adulthood, leading to negative long-term outcomes including substance-related morbidity: an empirical definition of its construct may inform the early detection of persistent pain trajectories. These secondary analyses of a classical twin study assessed whether headaches, back pains, abdominal pain, chest pains, stabbing/throbbing pain, and gastric pain/nausea, measured in 501 pairs across 5 waves between age 12 and 17 years, fit a unitary construct or constitute independent manifestations. We then assessed which symptoms were associated with a steady, "frequent pain" trajectory that is associated with risk for early opioid prescriptions. Item response theory results indicated that all 6 pain symptoms index a unitary construct. Binary logistic regressions identified "back pain" as the only symptom consistently associated with membership in the "frequent adolescent pain" trajectory (odds ratio: 1.66-3.38) at all 5 measurement waves. Receiver operating characteristic analyses computed the discriminating power of symptoms to determine participants' membership into the "frequent" trajectory: they yielded acceptable (0.7-0.8) to excellent (0.8-0.9) area under the curve values for all 6 symptoms. The highest area under the curve was attained by "back pain" at age 14 years (0.835); for multiple cut-off thresholds of symptom frequency, "back pain" showed good sensitivity/false alarm probability trade-offs, predominantly in the 13 to 15 years age range, to predict the "frequent pain" trajectory. These data support a unitary conceptualization and assessment of adolescent pain, which is advantageous for epidemiological, clinical, and translational purposes. Persistent back pain constitutes a sensitive indicator of a steady trajectory of adolescent pain.

The (limited) contribution of early childcare arrangements to social and academic development among Canadian children.

This study examined the longitudinal contribution of four different childcare arrangements attended during the preschool years to social behaviors and academic achievement up to age 15 years. Children participating in a Canadian longitudinal survey with available information on childcare attendance between ages 3 and 5 years (N = 6,852) were measured on multiple social behaviors (hyperactivity/inattention, depression/anxiety, disruptive behaviors) and academic outcomes (mathematic skills, academic achievement) across both childhood and adolescence. We conducted a propensity score matching analysis to control the selection bias for childcare attendance and performed generalized estimating equation models for panel data among matched groups. Our results showed no clear social or academic long-term advantage for Canadian children of attending any childcare arrangement in comparison to children being exclusively cared for by their parents. In contrast, children attending daycare centers had higher levels of hyperactivity/inattention until the age of 15 years. Children also had lower mathematic skills if attending daycare centers or informal childcare at preschool age, but this effect dissipated from childhood to adolescence. Interestingly, children from low-income families had higher levels of depression/anxiety if being cared for at home by someone other than their parents or relatives. This finding supports the dual-risk hypothesis suggesting that children from already impoverished families and attending informal childcare in their own home are at greater risk for internalizing difficulties. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Trajectories of pain and anxiety in a longitudinal cohort of adolescent twins.

BACKGROUND: Adolescence is critical to intercept chronic/persistent pain and decipher its association with anxiety. We ascertained adolescent pain trajectories, their demographic and clinical correlates, the longitudinal association with opiate prescriptions at age 19, and the etiology of the covariation between adolescent pain problems and anxiety symptoms. METHODS: Longitudinal assessment of: 6 common pain problems at age 12, 13, 14, 15, and 17 years; 7 common anxiety symptoms at age 12, 13, and 14 years; opiates' prescriptions at age 19, in the Quebec Newborn Twin Study birth cohort of 667 twin pairs born between 1995-1998. RESULTS: Analyses yielded three trajectories of: "none-to-minimal" (34.3%), "sporadic" (56.7%), and "frequent" (9.0%) pain problems between age 12-17. Anxiety (odds ratios [OR] ORage12 : 2.38; confidence interval [CI]: 1.26-4.47; ORage13 : 3.96; CI: 1.73-9.05; ORage14 : 5.45; CI: 2.67-11.11), the female sex (OR: 3.69; CI: 2.20-6.21), and lower socioeconomic status (OR: 0.87; CI: 0.77-0.98) were associated with the "frequent" compared to the "none-to-minimal" pain trajectory. Only the "frequent" pain trajectory predicted opioid prescriptions at age 19 (OR: 4.14; CI: 1.16-14.55). A twin bivariate latent growth curve model and a cross-lagged model showed that genetic factors and non-shared environmental factors common to both phenotypes influence the longitudinal association between anxiety and adolescent pain problems. CONCLUSIONS: The relatively common, adolescent "frequent pain" trajectory predicts early opioid prescriptions, and anxiety and adolescent pain share multiple etiological components. These data can inform diagnostic reasoning, clinical practice, and help reducing opioid prescriptions and abuse.

The nature of the association between number line and mathematical performance: An international twin study.

BACKGROUND: The number line task assesses the ability to estimate numerical magnitudes. People vary greatly in this ability, and this variability has been previously associated with mathematical skills. However, the sources of individual differences in number line estimation and its association with mathematics are not fully understood. AIMS: This large-scale genetically sensitive study uses a twin design to estimate the magnitude of the effects of genes and environments on: (1) individual variation in number line estimation and (2) the covariation of number line estimation with mathematics. SAMPLES: We used over 3,000 8- to 16-year-old twins from the United States, Canada, the United Kingdom, and Russia, and a sample of 1,456 8- to 18-year-old singleton Russian students. METHODS: Twins were assessed on: (1) estimation of numerical magnitudes using a number line task and (2) two mathematics components: fluency and problem-solving. RESULTS: Results suggest that environments largely drive individual differences in number line estimation. Both genes and environments contribute to different extents to the number line estimation and mathematics correlation, depending on the sample and mathematics component. CONCLUSIONS: Taken together, the results suggest that in more heterogeneous school settings, environments may be more important in driving variation in number line estimation and its association with mathematics, whereas in more homogeneous school settings, genetic effects drive the covariation between number line estimation and mathematics. These results are discussed in the light of development and educational settings.

Early developmental trajectories of number knowledge and math achievement from 4 to 10 years: Low-persistent profile and early-life predictors.

Little is known about the development of number knowledge (NK) and the antecedents of low-persistent NK profiles in early childhood. We documented the developmental trajectories of NK across the transition from preschool to elementary school, their predictive validity with respect to later math achievement, and the child and family early-life factors associated with low NK profiles. Children's NK was assessed four times at regular intervals between the ages 4 and 7 years in a large, representative population-based sample. Developmental trajectories of NK were established for 1597 children. These children were also assessed with respect to several features of their family environment at 5, 17, and 29 months, as well as their cognitive skills at age 41 months. Analyses revealed a best-fitting 4-trajectory model, characterized by Low-Increasing (10% of the children), Moderate-Increasing (39%), Moderate-Fast Increasing (32%) and High-Increasing (19%) groups. Children of these trajectory groups differed significantly with respect to math achievement at ages 8 and 10 years, with the Low-Increasing group persistently scoring lower than the other groups throughout these years. Children of Low-Increasing NK group were from household of lower income and father with low educational background, poorer early cognitive development, and more importantly, reduced visual-spatial skills and memory-span. Children displaying reduced cognitive abilities and impoverished living conditions early in life are at greater risk of low NK throughout late preschool and school entry, with ensuing difficulties in math achievement. They deserve early preventive attention to help alleviate later mathematic difficulties.

Twin classroom dilemma: To study together or separately?

There is little research to date on the academic implications of teaching twins in the same or different classroom. Consequently, it is not clear whether twin classroom separation is associated with positive or negative educational outcomes. As a result, parents and teachers have insufficient evidence to make a well-informed decision when twins start school. This study addresses two research questions: Are there average positive or negative effects of classroom separation? Are twins taught in different classes more different from each other than twins taught in the same class? Twin pairs from two large representative samples from Quebec (Canada) and the United Kingdom were evaluated across a large age range (7 to 16 years) on academic achievement, several cognitive abilities and motivational measures. Our results show almost no sizable positive or negative average effect of classroom separation on twins' achievement, cognitive ability and motivation. Twin pairs at age 12 (Quebec, Canada) and at age 16 (United Kingdom) were slightly more similar on achievement if placed in the same classroom, with slightly greater similarity among monozygotic twins than dizygotic twins. However, the few effects found were weak, and it remains unclear whether they result from classroom separation or other factors. These results suggest that in terms of educational outcomes, policymakers should not impose rigid guidelines to separate twin pairs during their education. The choice of whether to educate twin pairs together or separately should be up to parents, twins and teachers, in response to twins' individual needs. (PsycINFO Database Record