Childhood behavior problems and adverse economic outcomes: a 30-year population-based study of intergenerational income mobility.

BACKGROUND: The objectives of this study were to (a) assess the associations between early behavioral problems and intergenerational income mobility (i.e., the degree to which income status is transmitted from one generation to the next), (b) verify whether these associations are moderated by child sex, and (c) explore indirect effects of early behavioral problems on income mobility via high school graduation. METHODS: Data were drawn from the Quebec Longitudinal Study of Kindergarten Children (n = 3,020; 49.17% girls). Participants were followed from age 6 to 37 years. Measures included parents' and teachers' ratings of behavioral problems at age 6 years as well as participants' (ages 30-35 years) and their parents' (when participants were aged 10-19 years) income data obtained from tax return records. Regression models were used to predict upward and downward mobility (i.e., increased or decreased income status from one generation to the next) from attention-deficit/hyperactivity problems, conduct/opposition problems, depression/anxiety problems, prosociality, and the quality of children's relationship with their caregiver. Two-way interaction effects between behavioral problems and child sex were examined and indirect effect models including high school graduation as a mediator of these associations were conducted. RESULTS: Despite their higher educational attainment, females had lower incomes and experienced lower upward (but higher downward) income mobility than males. For both females and males, higher levels of attention-deficit/hyperactivity and conduct/opposition problems were associated with decreased odds of upward mobility, whereas higher levels of attention-deficit/hyperactivity were associated with increased odds of downward mobility. Attention-deficit/hyperactivity problems, conduct/opposition problems as well as low prosociality were associated with lower educational attainment (no high school diploma), which in turn was associated with increased odds of downward mobility. CONCLUSIONS: Results highlight the importance of providing intensive support to children with early behavioral problems as a means of improving educational attainment and intergenerational income mobility.

The interplay of maternal and paternal postpartum depressive symptoms with children's internalizing and externalizing symptoms from childhood to adolescence: does socioeconomic status matter? A longitudinal cohort study.

BACKGROUND: Maternal postpartum depression is an important risk factor for internalizing and externalizing problems in children. The role of concurrent paternal depression remains unclear, especially by socioeconomic status. This study examined independent and interactive associations of postpartum maternal and paternal depression with children's internalizing/externalizing symptoms throughout childhood and adolescence (ages 3.5-17 years). METHODS: We used data from the Québec Longitudinal Study of Child Development, a representative birth cohort (1997-1998) in Canada. Data included self-reported maternal and paternal depressive symptoms at 5 months' postpartum using the Center for Epidemiologic Studies Depression Scale. Internalizing and externalizing symptoms in children were reported by parents, teachers and children/adolescents using the Social Behaviour Questionnaire (ages 3.5-13 years) and the Mental Health and Social Inadaptation Assessment for Adolescents (ages 15-17 years). We used three-level mixed effects modelling to test associations after adjusting for confounding factors. RESULTS: With 168 single-parent families excluded, our sample consisted of 1,700 families with useable data. Of these, 275 (16.2%) families reported maternal depression (clinically elevated symptoms), 135 (7.9%) paternal depression and 39 (2.3%) both. In families with high socioeconomic status, maternal depression was associated with greater child internalizing (ß = .34; p < .001) and externalizing symptoms (ß = .22; p = .002), regardless of the presence/absence of paternal depression. In families with low socioeconomic status, associations with symptoms were stronger with concurrent paternal depression (internalizing, ß = .84, p < .001; externalizing, ß = .71, p = .003) than without (internalizing, ß = .30, p < .001; externalizing, ß = .24, p = .002). CONCLUSIONS: Maternal depression increases the risk for children's internalizing/externalizing problems in all socioeconomic contexts. In families with low socioeconomic status, risks were exacerbated by concurrent paternal depression. Postpartum depression, especially in low socioeconomic environments, should be a primary focus to optimize mental health across generations.

On executive functioning and childcare: The moderating role of parent-child interactions.

Childcare services are widely used by families and thereby exert an important influence on many young children. Yet, little research has examined whether childcare may impact the development of child executive functioning (EF), one of the pillars of cognitive development in early childhood. Furthermore, despite persisting hypotheses that childcare may be particularly beneficial for children who have less access to optimal developmental resources at home, research has yet to address the possibility that putative associations between childcare and EF may vary as a function of family factors. Among a sample of 180 mostly White middle-class families (91 girls), we examined if childcare participation in infancy was related to two aspects of EF (Delay and Conflict) at 3 years, and whether two aspects of maternal parenting behavior (sensitivity and autonomy support) moderated these associations. The results showed positive associations between participation in group-based childcare and Delay EF specifically among children of relatively less autonomy-supportive mothers. These findings suggest that out-of-home childcare services may play a protective role for children exposed to parenting that is less conducive to their executive development. RESEARCH HIGHLIGHTS: Little research has considered effects of childcare in infancy on executive functioning (EF). Long-standing hypothesis that childcare is more beneficial for children exposed to less sensitive and supportive parenting. We test interactions between maternal parenting and childcare participation in infancy in relation to EF at age 3 years. We find positive associations between participation in group-based childcare and Delay EF specifically among children of relatively less autonomy-supportive mothers.

Mechanisms and pathways linking kindergarten behavior problems with mid-life employment earnings for males from low-income neighborhoods.

Childhood behavior problems are associated with reduced labor market participation and lower earnings in adulthood, but little is known about the pathways and mechanisms that explain these associations. Drawing on a 33-year prospective birth cohort of White males from low-income backgrounds (n = 1040), we conducted a path analysis linking participants' teacher-rated behavior problems at age 6 years-that is, inattention, hyperactivity, aggression-opposition, and low prosociality-to employment earnings at age 35-39 years obtained from tax records. We examined three psychosocial mediators at age 11-12 years (academic, behavioral, social) and two mediators at age 25 years (non-high school graduation, criminal convictions). Our findings support the notion that multiple psychosocial pathways-especially low education attainment-link kindergarten behavior problems to lower employment earnings decades later.

Does early child negative emotionality moderate the association between maternal stimulation and academic readiness and achievement?

We investigated whether child temperament (negative emotionality, 5 months) moderated the association between maternal stimulation (5 months-2½ years) and academic readiness and achievement (vocabulary, mathematics, and reading). We applied structural equation modeling to the data from the Quebec Longitudinal Study of Child Development (N = 1121-1448; mostly Whites; 47% girls). Compared to children with low negative emotionality, those with high negative emotionality had higher levels of academic readiness (6 years) and mathematics achievement (7 years) when exposed to high levels of maternal stimulation (ß = 3.17, p < .01 and ß = 2.91, p < .01, respectively). The results support the differential susceptibility model whereby highly emotionally negative children were more susceptible to the influences of low and high levels of maternal stimulation in academic readiness and mathematics achievement's developments.

Childhood behavioral problems are associated with the intergenerational transmission of low education: a 16-year population-based study.

The intergenerational transmission of low educational attainment is well-documented, but little is known about how behavioral problems in childhood explain this association. Drawing upon a population-based cohort study (n = 3020) linked to administrative records, we investigated the extent to which inattentive, internalizing, externalizing, and prosocial behaviors at child ages 6-8 years accounted for associations between parental education and child's risk of failing to graduate from high school. We adjusted for economic, demographic, cognitive, and perinatal factors, as well as parental mental health. Using logistic regressions and the Karlson-Holm-Breen decomposition method, we found that childhood behaviors together explained 19.5% of the association between mother's education and child's high school graduation status at age 22/23, and 13.7% of the association between father's education and this same outcome. Inattentive behaviors were most strongly associated with failure to graduate from high school, while the role of other behaviors was modest or negligible. Inattentive behaviors may represent a mediational pathway between parental education and child education. Early interventions targeting inattentive behaviors could potentially enhance the prospects of intergenerational educational mobility.

Developmental Losses of Preschool Children Three Years into the COVID-19 Pandemic.

The COVID-19 pandemic and resulting mitigation measures have led to increased vulnerabilities in early child development. However, research is scarce and there are no studies on the persistence of these losses three years into the pandemic among young children. To fill in this gap, we examined census-like evaluations of school readiness carried out among preschoolers in Uruguay. The assessments were carried out among 5 cohorts of 5-year-olds: who were assessed prior to the pandemic (2018, 2019); during the pandemic (2020, 2021); and after the health emergency declaration ended in Uruguay (2022). A total of 180,984 teacher evaluations were included covering cognitive, motor and socio-emotional development, as well as attitudes toward learning. Overall, we found that scores in most spheres of child development decreased from before to during the pandemic in 2020 and 2021. In 2022, scores returned to pre-pandemic levels. Our findings suggest the recovery of developmental losses among cohorts of children in kindergarten took more than two years in a country that experienced a mild-to-moderate impact of the COVID-19 pandemic.

Differential Association of Preadolescent Risk Factors Across Developmental Patterns of Adolescent Concurrent Gambling Participation and Substance Use.

Early risk factors for gambling participation (GP) and substance use (SU) in adolescents have usually been studied separately, although these disorders were integrated into the same clinical category over a decade ago. This exploratory study aimed to investigate the early individual, parental, familial and social risk factors associated with developmental patterns of adolescent GP and SU in a population-representative cohort (N = 1594, 51.2% boys). Using a person-centered strategy and multiple assessments from age 12 to 17, six developmental patterns describing joint GP and SU courses were revealed. Non-substance users/non-gamblers served as the reference class in an integrated longitudinal-multivariate analysis framework examining 15 distinct risk factors. Results showed that a core of risk factors were common to all trajectory-classes of substance users with or without GP. For a similar level of SU, most of the risk factors associated with non-gambling users also affected their gambling peers. However, additional risk factors were specifically related to GP. Thus, substance users who also gamble were affected by a greater number of risk factors than non-gambling substance users. Findings are consistent with a developmental syndrome of addiction, which posits a shared etiology between different expressions of addiction as well as differences in risk factors that lead to distinct trajectories of addictive behaviors. They highlight the importance of considering both GP and SU for a comprehensive assessment of adolescents' level of risk with regard to addictive behaviors.

Revisiting the childcare-attachment question: under what conditions is childcare participation associated with mother-child attachment security?

Decades have passed since the controversy regarding the putative risks of childcare for mother-child attachment broke out. Yet, some uncertainty remains, as relevant studies have produced inconsistent evidence. Some have proposed that those conflicting findings may be due to the fact that the effects of childcare are conditioned on parenting. Accordingly, this study examined whether relations between childcare participation and mother-child attachment vary according to maternal sensitivity and autonomy support. In this sample of 236 mother-child dyads, there was no indication of main effects of childcare participation on attachment. There were, however, some interactive effects, such that the children who showed the least secure attachment behaviors were those who did not attend childcare and had either less sensitive or less autonomy-supportive mothers. The findings suggest that the effects of childcare on mother-child attachment are best understood in light of the parenting children receive at home.

Perinatal and early-life factors associated with stable and unstable trajectories of psychopathic traits across childhood.

BACKGROUND: This study aimed to identify perinatal and early-life factors associated with trajectories of psychopathic traits across childhood. METHODS: Participants were 1631 children (51.5% girls) from the Quebec Longitudinal Study of Child Development. A wide range of perinatal and early-life factors were assessed from pregnancy to age 2.5 years using medical files and mothers' reports. Psychopathic traits were assessed via teachers' reports at ages 6, 7, 8, 10, and 12 years. Latent class growth analyses and multinomial logistic regressions controlling for child sex were conducted. Two-way interaction effects between perinatal/early-life factors and child sex were explored. RESULTS: Four trajectories of psychopathic traits were identified: High-stable (4.48%), Increasing (8.77%), Decreasing (11.46%), and Low-stable (75.29%). A few perinatal factors and most child-level and family-level early-life factors significantly increased the odds of following the High-stable v. the Low-stable trajectory. Higher levels of psychotropic exposures during pregnancy, socioeconomic adversity, child's physical aggression, child's opposition, mother's depressive symptoms, and hostile parenting increased the likelihood of following the Increasing instead of the Low-stable trajectory. Higher socioeconomic adversity, mother's depressive symptoms, and inconsistent parenting were associated with membership to the High-stable instead of the Decreasing trajectory. Most associations were not moderated by child sex. CONCLUSIONS: These results shed light on the perinatal and early-life factors that are associated with specific pathways of psychopathic traits during childhood and suggest that different factors could be targeted to prevent the exacerbation (v. low and stable levels) or the stability at high levels (v. attenuation) of these traits.

Childhood externalizing, internalizing and comorbid problems: distinguishing young adults who think about suicide from those who attempt suicide.

BACKGROUND: While childhood externalizing, internalizing and comorbid problems have been associated with suicidal risk, little is known about their specific associations with suicidal ideation and attempts. We examined associations between childhood externalizing, internalizing and comorbid problems and suicidal ideation (without attempts) and attempts by early adulthood, in males and females. METHOD: Participants were from the Quebec Longitudinal Study of Kindergarten Children, a population-based study of kindergarteners in Quebec from 1986 to 1988 and followed-up until 2005. We captured the co-development of teacher-rated externalizing and internalizing problems at age 6-12 using multitrajectories. Using the Diagnostic Interview Schedule administered at age 15 and 22, we identified individuals (1) who never experienced suicidal ideation/attempts, (2) experienced suicidal ideation but never attempted suicide and (3) attempted suicide. RESULTS: The identified profiles were no/low problems (45%), externalizing (29%), internalizing (11%) and comorbid problems (13%). After adjusting for socioeconomic and familial characteristics, children with externalizing (OR 2.00, CI 1.39-2.88), internalizing (OR 2.34, CI 1.51-3.64) and comorbid (OR 3.29, CI 2.05-5.29) problems were at higher risk of attempting suicide (v. non-suicidal) by age 22 than those with low/no problems. Females with comorbid problems were at higher risk of attempting suicide than females with one problem. Childhood problems were not associated with suicidal ideation. Externalizing (OR 2.01, CI 1.29-3.12) and comorbid problems (OR 2.28, CI 1.29-4.03) distinguished individuals who attempted suicide from those who thought about suicide without attempting. CONCLUSION: Childhood externalizing problems alone or combined with internalizing problems were associated with suicide attempts, but not ideation (without attempts), suggesting that these problems confer a specific risk for suicide attempts.

Mental health comorbidities following peer victimization across childhood and adolescence: a 20-year longitudinal study.

BACKGROUND: Peer victimization is associated with a wide range of mental health problems in youth, yet few studies described its association with mental health comorbidities. METHODS: To test the association between peer victimization timing and intensity and mental health comorbidities, we used data from 1216 participants drawn from the Quebec Longitudinal Study of Child Development, a population-based birth cohort. Peer victimization was self-reported at ages 6-17 years, and modeled as four trajectory groups: low, childhood-limited, moderate adolescence-emerging, and high-chronic. The outcomes were the number and the type of co-occurring self-reported mental health problems at age 20 years. Associations were estimated using negative binomial and multinomial logistic regression models and adjusted for parent, family, and child characteristics using propensity score inverse probability weights. RESULTS: Youth in all peer victimization groups had higher rates of co-occurring mental health problems and higher likelihood of comorbid internalizing-externalizing problems [odds ratios ranged from 2.06, 95% confidence interval (CI) 1.52-2.79 for childhood-limited to 4.34, 95% CI 3.15-5.98 for high-chronic victimization] compared to those in the low victimization group. The strength of these associations was highest for the high-chronic group, followed by moderate adolescence-emerging and childhood-limited groups. All groups also presented higher likelihood of internalizing-only problems relative to the low peer victimization group. CONCLUSIONS: Irrespective of timing and intensity, self-reported peer victimization was associated with mental health comorbidities in young adulthood, with the strongest associations observed for high-chronic peer victimization. Tackling peer victimization, especially when persistent over time, could play a role in reducing severe and complex mental health problems in youth.

Medical conditions and Attention-Deficit/Hyperactivity Disorder symptoms from early childhood to adolescence.

The comorbidity between physical and mental health conditions is challenging and frequently goes unrecognized in practice. Associations between Attention-Deficit/Hyperactivity Disorder (ADHD) and physical conditions have been reported in youth. However, prior research failed to: (1) address the patterns of associations in early childhood, middle childhood, and adolescence within the same population sample; (2) consider a large set of physical disorders at the same time; (3) take confounders into account. Our goal was to assess the associations between ADHD symptoms and a broad set of physical conditions across developmental periods. This birth cohort study (n = 2057) is the first to explore the associations between ADHD and a wide range of medical conditions by encompassing the whole early development from 5 months to 17 years in the same sample and relying on innovative network analyses. We found significant associations between ADHD symptoms and several physical conditions, some of which were observed in early childhood, middle childhood, and adolescence (e.g., asthma, sleep problems) or were confounded by socioeconomic status or psychiatric comorbidities (e.g., body mass index, dental caries). The study calls for an effective integrated care model encompassing mental and general healthcare across the developmental period.

Uncovering the genetic architecture of broad antisocial behavior through a genome-wide association study meta-analysis.

Despite the substantial heritability of antisocial behavior (ASB), specific genetic variants robustly associated with the trait have not been identified. The present study by the Broad Antisocial Behavior Consortium (BroadABC) meta-analyzed data from 28 discovery samples (N = 85,359) and five independent replication samples (N = 8058) with genotypic data and broad measures of ASB. We identified the first significant genetic associations with broad ASB, involving common intronic variants in the forkhead box protein P2 (FOXP2) gene (lead SNP rs12536335, p = 6.32 × 10-10). Furthermore, we observed intronic variation in Foxp2 and one of its targets (Cntnap2) distinguishing a mouse model of pathological aggression (BALB/cJ strain) from controls (BALB/cByJ strain). Polygenic risk score (PRS) analyses in independent samples revealed that the genetic risk for ASB was associated with several antisocial outcomes across the lifespan, including diagnosis of conduct disorder, official criminal convictions, and trajectories of antisocial development. We found substantial genetic correlations of ASB with mental health (depression rg = 0.63, insomnia rg = 0.47), physical health (overweight rg = 0.19, waist-to-hip ratio rg = 0.32), smoking (rg = 0.54), cognitive ability (intelligence rg = -0.40), educational attainment (years of schooling rg = -0.46) and reproductive traits (age at first birth rg = -0.58, father's age at death rg = -0.54). Our findings provide a starting point toward identifying critical biosocial risk mechanisms for the development of ASB.

Polygenic risk score and peer victimisation independently predict depressive symptoms in adolescence: results from the Quebec Longitudinal Study of Children Development.

BACKGROUND: Peer victimisation has been associated with depressive symptoms during adolescence, however not all peer victimised adolescents will exhibit such symptoms. This study tested whether having a genetic predisposition to developing depression increased the risk of experiencing depressive symptoms in peer victimised youth. To date, no study has explored such gene-environment interaction using a polygenic risk score for depression (PRS-depression) in the context of peer victimisation and depressive symptoms in adolescence. METHODS: The sample included 748 participants born in 1997/98 from the Quebec Longitudinal Study of Child Development with genotype data and prospectively collected information on peer victimisation (12-13 years) obtained from both self- and teacher-reports, as well as self-reported depressive symptoms (15-17 years). The PRS-depression was based on the genome-wide association meta-analysis of broad depression by Howard et al. (2019). RESULTS: Self- and teacher-reported peer victimisation in early adolescence were both associated with depressive symptoms in adolescence (ß = 0.34, p < .001; ß = 0.14, p = .001 respectively), and this association remained significant when accounting for PRS-depression (ß = 0.33, p < .001; ß = 0.13, p = .002 respectively). PRS-depression was independently associated with depressive symptoms, but there was no significant PRS-depression by peer victimisation interaction (self-reported and teacher-reported). PRS-depression was correlated with self-reported, but not teacher-reported, peer victimisation. CONCLUSIONS: Our findings suggested that a partial measure of an individual's genetic predisposition to depression, as measured by PRS-depression, and being exposed to peer victimisation (self- and teacher-reported) were independently associated with depressive symptoms in adolescence. Furthermore, PRS-depression did not exacerbate the risk of depressive symptoms among adolescents who had been peer victimised. Lastly, we found evidence of a gene-environment correlation between PRS-depression and self-reported peer victimisation. Future studies are needed to replicate this finding and to further understand the role of genetic predispositions in experiencing depressive symptoms following peer victimisation.

Nocturnal sleep duration trajectories in early childhood and school performance at age 10 years.

Sleep plays a fundamental role in brain development and resultant functions. The aim was to verify whether nocturnal sleep duration during early childhood has long-term associations with academic achievement at age 10 years. The present study is part of the Quebec Longitudinal Study of Child Development, a representative cohort of infants born in 1997-1998 in the province of Quebec, Canada. Children with known neurological conditions were excluded from this cohort. Four trajectories of parent-reported nocturnal sleep duration at ages 2.5, 3, 4, 5 and 6 years were determined using a SAS procedure named PROC TRAJ. Sleep duration at age 10 years was also reported. Teachers provided data on academic performance when the children were age 10 years. These data were available for 910 children (430 boys, 480 girls; 96.6% Caucasians). Univariate and multivariable logistic regressions were performed using SPSS. Children who slept less than 8 hr per night at 2.5 years but normalized later on (Traj1) had three-five times the odds of having grades below the class average in reading, writing, mathematics and science compared with children who slept sufficiently (Traj3-4: 10-11 hr per night). Children who slept about 9 hr per night throughout childhood (Traj2) had two-three times the odds of being below the class average in mathematics and science. Sleep duration at age 10 years was not correlated with the academic performance. These results point to the presence of a very important early period during which sufficient sleep is needed to fine-tune the functions necessary for academic achievement later on.

Do more hours in center-based care cause more externalizing problems? A cross-national replication study.

Whether high quantities of center-based care cause behavior problems is a controversial question. Studies using covariate adjustment for selection factors have detected relations between center care and behavior problems, but studies with stronger internal validity less often find such evidence. We examined whether within-child changes in hours in center-based care predicted changes in externalizing problems in toddlers and preschoolers (N = 10,105; 49% female; data collection 1993-2012) in seven studies, including from Germany, Netherlands, Norway, two from Canada and two from the U.S. Race/ethnicity data were only collected in the United States (57% and 80% White; 42% and 13% African-American; 1.2% and 5% Latinx). Meta-analyses showed no association (r = .00, p = .88) between hours in center-based care and externalizing problems.

Adolescents' internalizing symptoms predict dating violence victimization and perpetration 2 years later.

The aim of this longitudinal study was to examine bidirectional associations of adolescents' internalizing symptoms with dating violence victimization and perpetration. We conducted secondary analyses of the Québec Longitudinal Study of Child Development data (n = 974). Each adolescent completed items from the Conflict Tactics Scale (at ages 15 and 17 years) to assess psychological, physical, and sexual dating violence victimization and perpetration in the past 12 months. Adolescents' symptoms of depression and general anxiety in the past 12 months were self-reported (at ages 15 and 17 years) using The Mental Health and Social Inadaptation Assessment for Adolescents. There were concurrent associations of adolescents' internalizing symptoms with dating violence victimization and perpetration. Internalizing symptoms at age 15 years were positively associated with dating violence victimization and perpetration 2 years later in both males and females, even after adjusting for baseline characteristics. However, neither dating violence victimization nor perpetration at age 15 years was associated with internalizing symptoms 2 years later. For males and females, internalizing symptoms put adolescents at risk for future dating violence victimization and perpetration. Interventions that target internalizing symptoms may have the potential to decrease subsequent dating violence.

Behaviors in kindergarten are associated with trajectories of long-term welfare receipt: A 30-year population-based study.

This study examines the link between behavior in kindergarten and adult-life welfare receipt. Teacher-rated behavioral assessments were obtained for inattention, hyperactivity, aggression-opposition, anxiety, and prosociality when children (n=2960) were aged 5-6 years and linked to their tax return records from age 18-35 years. We used group-based based trajectory modeling to identify distinct trajectories of welfare receipt and multinomial logistic regression models to examine the association between behaviors and trajectory group membership. The child's sex, IQ, and family background were adjusted for. Four trajectories of welfare receipt were identified: low (n = 2,390, 80.7%), declining (n = 260, 8.8%), rising (n = 150, 5.2%), and chronic (n = 160, 5.4%). Relative to the low trajectory, inattention and aggression-opposition at age 6 years were associated with increased risk of following a declining, rising, and chronic trajectory of welfare receipt, independent of hyperactivity and anxiety. Prosocial behaviors were independently associated with a lower risk of following a chronic trajectory. This study shows that kindergarten children exhibiting high inattention and aggression-opposition and low prosocial behaviors may be at increased risk of long-term welfare receipt in adulthood. The implications for early screening, monitoring, and prevention are discussed.

Protocol for the Open Sky School: a two-arm clustered randomized controlled trial to test the effectiveness of a nature-based intervention on mental health of elementary school children.

BACKGROUND: This article outlines the protocol for a trial to test the effectiveness of a nature-based intervention called Open Sky School to reduce mental health problems among elementary school children. Experimental studies show that contact with nature (e.g. walks in parks) improve mental health. A growing number of teachers have been applying outdoor education within the regular school curriculum and evidence suggests that such teaching methods could improve students' mental health but a randomized controlled trial has never been conducted. METHODS: A two-arm clustered randomized controlled trial will be conducted in elementary schools across Québec, Canada. Following informed consent by teachers, parents and students, schools will be randomly assigned 1:1 to the intervention or the control group with a total of 2500 5-6th grade students and 100 teachers expected to participate. The intervention will take place outdoors in a green-space (2 h per week for 12 weeks) and include a toolkit of 30 activities to foster well-being (e.g. mindfulness) and academic competencies (e.g. mathematics). Questionnaires will be administered to teachers and students before, immediately after and 3 months after the intervention. The primary outcome will be reductions of mental health problems in children from pre-to-post test (Social Behavior Questionnaire: self and teacher reports). Secondary outcomes include depression, positive and negative affect, nature connectedness, and pro-environmental behaviors among children. We will explore, immediate benefits on teacher's well-being and positive and negative affect and sustained benefits among students at 3 months follow-up. For the primary outcome, we will explore moderators including child's sex, child's disability status, the green-space of neighbourhoods, the school's socio-economic position and teacher's experience. DISCUSSION: In conducting the first randomized controlled trial of the Open Sky School, our results could provide empirical evidence on the effectiveness of nature-based interventions in reducing mental health problems among elementary school children. TRIAL REGISTRATION: This study was registered with clinicaltrials.gov: NCT05662436 on December 22, 2022.