Combinations of Physical Activity, Sedentary Behavior, and Sleep Duration and Their Associations With Physical, Psychological, and Educational Outcomes in Children and Adolescents: A Systematic Review.

We conducted a systematic review to evaluate combinations of physical activity, sedentary behavior, and sleep duration (defined as "movement behaviors") and their associations with physical, psychological, and educational outcomes in children and adolescents. MEDLINE, CINAHL, PsychInfo, SPORTDiscus, PubMed, EMBASE, and ERIC were searched in June 2020. Included studies needed to 1) quantitatively analyze the association of 2 or more movement behaviors with an outcome, 2) analyze a population between 5 and 17 years of age, and 3) include at least an English abstract. We included 141 studies. Most studies included the combination of physical activity and sedentary behavior in their analyses. Sleep was studied less frequently. In combination, a high level of physical activity and a low level of sedentary behavior were associated with the best physical health, psychological health, and education-related outcomes. Sleep was often included in the combination that was associated with the most favorable outcomes. Sedentary behavior had a stronger influence in adolescents than in children and tended to be associated more negatively with outcomes when it was defined as screen time than when defined as overall time spent being sedentary. More initiatives and guidelines combining all 3 movement behaviors will provide benefit with regard to adiposity, cardiometabolic risk factors, cardiorespiratory fitness, muscular physical fitness, well-being, health-related quality of life, mental health, academic performance, and cognitive/executive function.

Reliability of GENEActiv accelerometers to estimate sleep, physical activity, and sedentary time in children.

BACKGROUND: Reliable estimates of habitual sleep, physical activity, and sedentary time are essential to investigate the associations between these behaviours and health outcomes. While the number of days needed and hours/day for estimates of physical activity and sedentary time are generally known, the criteria for sleep estimates are more uncertain. The objective of this study was to identify the number of nights needed to obtain reliable estimates of habitual sleep behaviour using the GENEActiv wrist worn accelerometer. The number of days to obtain reliable estimate of physical activity was also examined. METHODS: Data was used from a two-year longitudinal study. Children wore an accelerometer for up to 8 days 24 h/day across three timepoints. The sample included 2,745 children (51 % girls) between the ages of 7-12-years-old (mean = 9.8 years, SD = 1.1 year) with valid accelerometer data from any timepoint. Reliability estimates were calculated for sleep duration, sleep efficiency, sleep onset, wake time, time in bed, light physical activity, moderate physical activity, moderate-to-vigorous physical activity, vigorous physical activity, and sedentary time. RESULTS: Intraclass correlations and the Spearman Brown prophecy formula were used to determine the nights and days needed for reliable estimates. We found that between 3 and 5 nights were needed to achieve acceptable reliability (ICC = 0.7) in sleep outcomes, while physical activity and sedentary time outcomes required between 3 and 4 days. CONCLUSIONS: To obtain reliable estimates, researchers should consider these minimum criteria when designing their studies and prepare strategies to ensure sufficient wear time compliance.

Maternal Judgments of Child Numeracy and Reading Ability Predict Gains in Academic Achievement and Interest.

In a representative longitudinal sample of 2,602 Australian children (52% boys; 2% Indigenous; 13% language other than English background; 22% of Mothers born overseas; and 65% Urban) and their mothers (first surveyed in 2003), this article examined if maternal judgments of numeracy and reading ability varied by child demographics and influenced achievement and interest gains. We linked survey data to administrative data of national standardized tests in Year 3, 5, and 7 and found that maternal judgments followed gender stereotype patterns, favoring girls in reading and boys in numeracy. Maternal judgments were more positive for children from non-English speaking backgrounds. Maternal judgments predicted gains in children's achievement (consistently) and academic interest (generally) including during the transition to high school.

School-based interventions modestly increase physical activity and cardiorespiratory fitness but are least effective for youth who need them most: an individual participant pooled analysis of 20 controlled trials.

OBJECTIVES: To determine if subpopulations of students benefit equally from school-based physical activity interventions in terms of cardiorespiratory fitness and physical activity. To examine if physical activity intensity mediates improvements in cardiorespiratory fitness. DESIGN: Pooled analysis of individual participant data from controlled trials that assessed the impact of school-based physical activity interventions on cardiorespiratory fitness and device-measured physical activity. PARTICIPANTS: Data for 6621 children and adolescents aged 4-18 years from 20 trials were included. MAIN OUTCOME MEASURES: Peak oxygen consumption (VO2Peak mL/kg/min) and minutes of moderate and vigorous physical activity. RESULTS: Interventions modestly improved students' cardiorespiratory fitness by 0.47 mL/kg/min (95% CI 0.33 to 0.61), but the effects were not distributed equally across subpopulations. Girls and older students benefited less than boys and younger students, respectively. Students with lower levels of initial fitness, and those with higher levels of baseline physical activity benefitted more than those who were initially fitter and less active, respectively. Interventions had a modest positive effect on physical activity with approximately one additional minute per day of both moderate and vigorous physical activity. Changes in vigorous, but not moderate intensity, physical activity explained a small amount (~5%) of the intervention effect on cardiorespiratory fitness. CONCLUSIONS: Future interventions should include targeted strategies to address the needs of girls and older students. Interventions may also be improved by promoting more vigorous intensity physical activity. Interventions could mitigate declining youth cardiorespiratory fitness, increase physical activity and promote cardiovascular health if they can be delivered equitably and their effects sustained at the population level.

Is Self-Compassion Selfish? The Development of Self-Compassion, Empathy, and Prosocial Behavior in Adolescence.

Both self-compassion and empathy have been theorized to promote prosociality in youth, but there is little longitudinal data examining this possibility. We assessed self-compassion, empathy, and peer-rated prosociality yearly, in a cohort of 2,078 youth across 17 schools (M age at T1 = 14.65 years; 49.2% female), as they progressed from Grade 9-12. We utilized multi-level modeling to predict prosocial behavior, nested within students, classes, and schools. We found that self-compassion and empathy uniquely predicted peer-rated prosocial behavior. However, only empathy predicted increases in prosocial behavior across time. While self-compassion is not selfish, it does not appear to facilitate the development of kindness toward adolescent peers. Self-compassion may help to buffer against possible negative effects of empathic distress.

Confirmatory Factor Analysis (CFA), Exploratory Structural Equation Modeling (ESEM), and Set-ESEM: Optimal Balance Between Goodness of Fit and Parsimony.

CFAs of multidimensional constructs often fail to meet standards of good measurement (e.g., goodness-of-fit, measurement invariance, and well-differentiated factors). Exploratory structural equation modeling (ESEM) represents a compromise between exploratory factor analysis' (EFA) flexibility, and CFA/SEM's rigor and parsimony, but lacks parsimony (particularly in large models) and might confound constructs that need to be kept separate. In Set-ESEM, two or more a priori sets of constructs are modeled within a single model such that cross-loadings are permissible within the same set of factors (as in Full-ESEM) but are constrained to be zero for factors in different sets (as in CFA). The different sets can reflect the same set of constructs on multiple occasions, and/or different constructs measured within the same wave. Hence, Set-ESEM that represents a middle-ground between the flexibility of traditional-ESEM (hereafter referred to as Full-ESEM) and the rigor and parsimony of CFA/SEM. Thus, the purposes of this article are to provide an overview tutorial on Set-ESEM, juxtapose it with Full-ESEM, and to illustrate its application with simulated data and diverse "real" data applications with accessible, heuristic explanations of best practice.

Discrimination as a frame-of-reference effect in overlapping friendship communities of ethnically diverse youth.

OBJECTIVES: To what extent is the frame of reference of overlapping friendship communities important for young people's feelings of discrimination and subjective well-being? That is, do youth feel better or worse to the extent that they feel less or more discrimination than their friends? METHOD: Participants (N = 898; Mage = 14.13; SDage = 3.37; 46% females; 46% Whites; 20% Indigenous; 34% other minorities) were high school students of three ethnically diverse, low socioeconomic status public schools in New South Wales, Australia. Cross-sectional data were collected to measure felt discrimination, mental health, subjective well-being, social support, and nominations of close friends. A state-of-the-art method of clustering links was used to identify overlapping friendship communities, and multiple membership multilevel models were run to examine whether community-level discrimination moderated the link between individual-level discrimination and well-being. RESULTS: When the community level discrimination was low, there was no well-being related cost or benefit of individual-level discrimination. But when the community-level discrimination was high, individuals in those communities who themselves felt low discrimination had better well-being than individuals who themselves felt high discrimination. CONCLUSIONS: We provide evidence for a frame-of-reference effect involving discrimination. Individuals' relative standing in their friendship communities with high group-level discrimination reliably predicted the individuals' well-being levels, regardless of ethnicity. The results highlight the importance of identifying overlapping friendship communities for understanding the dynamics of discrimination and well-being of ethnically diverse youth. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Type of screen time moderates effects on outcomes in 4013 children: evidence from the Longitudinal Study of Australian Children.

BACKGROUND: Excessive engagement with digital screens is harmful to children's health. However, new evidence suggests that exposure at moderate levels may not be harmful and may even provide benefit. Therefore, our objective was to determine if there are curvilinear relationships between different types of screen time and a diverse set of outcomes, including health and education. METHODS: We address our objective using a repeated measures design. Children (N = 4013), initially aged 10-11 were assessed every 2 years between 2010 and 2014. Children's screen time behavior was measured using time-use diaries, and categorized into five types: social, passive, interactive, educational, or other. We used measures of children's physical health, health-related quality of life, socio-emotional outcomes, and school achievement. The analysis plan was pre-registered. Models were adjusted for gender, socio-economic status, ethnicity, number of siblings, and housing factors. RESULTS: There were linear associations between total screen time and all outcomes, such that more screen time was associated with worse outcomes. However, there was variability when examined by screen time type. Passive screen time (e.g., TV) was associated with worse outcomes, educational screen time (e.g., computer for homework) was associated with positive educational outcomes and had no negative relations with other outcomes. Interactive screen time (e.g., video games) had positive associations with educational outcomes but negative associations with other outcomes. In all instances, these significant associations were small or very small, with standardised effects < 0.07. We found little evidence of curvilinear relationships. CONCLUSIONS: The small effects of screen time on children's outcomes appear to be moderated by the type of screen time. Policy makers, educators, and parents should consider the type of screen time when considering the benefits and harms of use.

A monitoring system to provide feedback on student physical activity during physical education lessons.

School-based physical education (PE) provides opportunities to accumulate moderate-to-vigorous physical activity (MVPA), but many students are insufficiently active during PE lessons. Providing teachers with feedback regarding their students' physical activity may increase the effectiveness of PE for achieving MVPA goals, but existing physical activity monitoring technologies have limitations in class environments. Therefore, the purpose of this study was to develop and validate a system capable of providing feedback on PE lesson MVPA. Equations for translating step counts to %MVPA were derived from measures in 492 students who concurrently wore an ActiGraph GT3X+ (ActiGraph) and Yamax pedometer (Yamax) during a PE lesson. To enhance feedback availability during PE lessons, we then developed a bespoke monitoring system using wireless tri-axial pedometers (HMM) and a smart device app. After developing and testing the monitoring system, we assessed its validity and reliability in 100 students during a PE lesson. There was a strong correlation of 0.896 between step counts and accelerometer-determined %MVPA and quantile regression equations showed good validity for translating step counts to %MVPA with a mean absolute difference of 5.3 (95% CI, 4.4-6.2). The physical activity monitoring system was effective at providing %MVPA during PE lessons with a mean difference of 1.6 ± 7.1 compared with accelerometer-determined %MVPA (7% difference between the two measurement methods). Teachers and students can use a smart device app and wireless pedometers to conveniently obtain feedback during PE lessons. Future studies should determine whether such technologies help teachers to increase physical activity during PE lessons.

Compulsive internet use and the development of self-esteem and hope: A four-year longitudinal study.

OBJECTIVE: Compulsive internet use (CIU) has been linked to decrements in mental health and well-being. However, relatively little is known about how CIU relates to evaluations of the self, and in particular, whether CIU is antecedent to or is a consequence of negative evaluations of one's social worth (self-esteem) and general efficacy (hope). To examine this, we explored the longitudinal relations between CIU and the development of self-esteem and hope among adolescents over a four-year period. METHOD: Two thousand eight hundred and nine adolescents completed measures yearly from Grade 8 (MAge = 13.7) to Grade 11. Autoregressive cross-lagged structural equation models were used to test whether CIU influenced or was influenced by self-esteem and hope. RESULTS: We found consistent support for a CIU-as-antecedent model. CIU preceded reductions in trait hope, and small reductions in self-esteem. In contrast, we did not find evidence for a CIU-as-consequence model: low self-esteem and hope did not predict increases in CIU over time. CONCLUSIONS: Our findings suggest that CIU has negative consequences for young people's feelings of goal-efficacy, and that interventions that address the compulsive use of the internet are likely to strengthen hope and self-esteem among young people.

Domain-specific physical activity and affective wellbeing among adolescents: an observational study of the moderating roles of autonomous and controlled motivation.

BACKGROUND: Abundant evidence demonstrates a relationship between physical activity and mental wellbeing. However, the strength of the relationship is not consistent. Factors contributing to variation in the strength of association are not well understood and, therefore, it remains difficult to optimize physical activity to ensure the strongest possible relationship with mental health. Self-determination theory suggests that more autonomously motivated behaviors lead to better mental health outcomes, when compared to more controlled behaviors. Therefore, we examined whether autonomous and controlled motivation moderated the relationships between physical activity and affective wellbeing within two domains (i.e., leisure-time and active travel). METHODS: Between February and April 2014, adolescents (N = 1632, M age = 12.94 years, SD = 0.54, 55% male) wore an accelerometer across seven-days and completed self-report measures of leisure-time physical activity and active travel. They also completed two measures of motivation (towards leisure-time physical activity and active travel) and an affective wellbeing measure. RESULTS: Structural equation modeling revealed that greater self-reported leisure-time physical activity was associated with greater positive affect (ß = .29) and less negative affect (ß = -.19) and that motivation did not moderate these relationships. Self-reported active travel had no linear relationship with affective wellbeing, and motivation did not moderate these relationships. Accelerometer-measured leisure-time physical activity had no relationship with positive affect but, had a weak inverse association with negative affect (ß = -.09), and neither relationship was moderated by motivation. Accelerometer-measured active travel had no association with positive affect; however, autonomous motivation significantly moderated this association such that active travel had a positive association with positive affect when autonomous motivation was high (ß = .09), but a negative association when autonomous motivation was low (ß = -.07). Accelerometer-measured active travel had no association with negative affect. Despite some significant moderation effects, motivation did not consistently moderate the relationship between all physical activity variables (leisure-time and active travel, and self-report and accelerometer) and affective outcomes. CONCLUSIONS: Tailoring physical activity interventions and guidelines to prioritize leisure-time ahead of other life domains could benefit wellbeing. Promoting autonomous participation in active travel may also be associated with increased wellbeing among adolescents.

A worthy self is a caring self: Examining the developmental relations between self-esteem and self-compassion in adolescents.

OBJECTIVE: Self-compassion has been framed as a healthy alternative to self-esteem, as it is nonevaluative. However, rather than being alternatives, it may be that the two constructs develop in a mutually reinforcing way. The present study tested this possibility among adolescents. METHOD: A large adolescent sample (N = 2,809; 49.8% female) reported levels of trait self-esteem and self-compassion annually for 4 years. Autoregressive cross-lagged structural equation models were used to estimate the reciprocal longitudinal relations between the two constructs. RESULTS: Self-esteem consistently predicted changes in self-compassion across the 4 years of the study, but not vice versa. CONCLUSIONS: Self-esteem appears to be an important antecedent of the development of self-compassion, perhaps because the capacity to extend compassion toward the self depends on one's appraisals of worthiness. These findings add important insights to our theoretical understanding of the development of self-compassion.

Development of Friendship and Task Values in a New School: Friend Selection for the Arts and Physical Education but Socialization for Academic Subjects.

Friends provide important social contexts for student development. Research has shown that adolescent friends are similar to each other in their interest and values for different school subjects. Yet our current understanding does not extend to knowing whether selection, deselection, or socialization processes are responsible for this phenomena. Without this knowledge, it is very difficult for parents, teachers, and schools to know how and when to intervene. This study investigated selection, deselection, and socialization effects on adolescent students' task values for academic (languages, math and science, and social sciences) and non-academic subject areas (the arts and physical education). A social network approach was used to examine two waves of annual data collected from school-based networks of adolescents in the first and second years of high school education in Finland (N = 1419; female = 48.6%; mean age at first measurement point = 16). The results revealed that adolescents tended to select friends with similar levels of task values (friend selection) for the arts and physical education, but friends did not become more similar in these areas over time (friend socialization). In contrast, there was evidence of friend socialization, but not friend selection, for the academic school subjects. Across all subjects, differences in task values did not predict friendship dissolution (friend deselection). These findings suggest that to a significant extent, students make agentic choices in developing friendship with schoolmates based on their task values in non-academic subjects. The resultant friend contexts that individuals created, in turn, affected their task values in academic subject areas. These results shed light on the complexity of friend effect mechanisms on task values at the subject domain-specific level.

When Empathy Matters: The Role of Sex and Empathy in Close Friendships.

Based on prior theory and research (Ciarrochi & Heaven, 2009; Eagly & Wood, 1999), we hypothesized that the link between empathy and friendship would be moderated by sex: Girls will nominate empathic boys as friends, whereas boys will not tend to nominate empathic girls. We collected measures of empathy, friendship social support, and close friendship nominations in grade 10 across 1,970 students in 16 schools (Mage = 15.70, SD = .44; males = 993, females = 977). Multilevel models revealed that boys high in cognitive empathy attracted an average of 1.8 more girl friendship nominations than did their low empathy counterparts, whereas empathic girls did not attract a greater number of opposite-sex friends. In addition, the more friendship nominations a boy received from either boys or girls, the more they felt supported by their friends; the number of friendship nominations received by girls, in contrast, had no effect on their felt support by friends. Regardless of the quantity of friendship nominations, empathy was linked to more supportive friendships for both males and females. These results inform a contextual understanding of the role of empathy in selecting and maintaining friendships.

Cognitive Defusion Predicts More Approach and Less Avoidance Coping With Stress, Independent of Threat and Self-Efficacy Appraisals.

OBJECTIVE: Recent evidence suggests that the way in which individuals relate to their aversive thoughts predicts behavioral effectiveness more than the content of such thoughts. This article is among the first to explore whether this is true for coping with stressful events. METHOD: Three studies with emerging adults (Study 1, N = 202) and adults (Study 2, N = 201; Study 3, N = 141) tested whether changes in how individuals relate to their stress-related thoughts, measured using the individual-difference construct of cognitive defusion, predicted more approach and less avoidance coping behavior, controlling for stress-related appraisals. RESULTS: We found that cognitive defusion predicted more approach coping (Studies 1 and 3) and less avoidance coping (Studies 2 and 3) following laboratory-induced stress (Study 1), naturally occurring monthly stress (Study 2), and daily stress (Study 3). These effects occurred independently of the effects of threat appraisals (Studies 1-3) and self-efficacy appraisals (Study 3) on coping responses. CONCLUSIONS: Cognitive defusion may be an important individual-difference predictor of coping behavior, adding to established theories of coping such as Lazarus and Folkman's (1987) transactional theory.

Emotion regulation strategies in daily life: mindfulness, cognitive reappraisal and emotion suppression.

Most empirical studies of emotion regulation have relied on retrospective trait measures, and have not examined the link between daily regulatory strategies and every day emotional well-being. We used a daily diary methodology with multilevel modelling data analyses (n = 187) to examine the influence of three emotion regulation strategies (mindfulness, cognitive reappraisal and emotion suppression) on the experience of daily negative and positive affect. Our results suggested that daily mindfulness was associated with lower negative and higher positive affect whereas the converse pattern was found for daily emotion suppression; cognitive reappraisal was related to daily positive, but not negative affect. When daily mindfulness, suppression and reappraisal were included in the same models, these strategies predicted unique variance in emotional well-being. Random slope analyses revealed substantial variability in the utility of these strategies. Indeed the presumably "adaptive" cognitive reappraisal strategy seemed to confer no benefit to the regulation of negative affect in approximately half the sample. Additional analyses revealed that age moderates the effect of cognitive reappraisal on daily negative affect: Higher use of reappraisal was associated with more negative affect for adolescents (aged 17 to 19) but became associated with less negative affect with increasing age. We interpret these results in line with a contextual view of emotion regulation where no strategy is inherently "good" or "bad".

Reciprocal Relationships between Teacher Ratings of Internalizing and Externalizing Behaviors in Adolescents with Different Levels of Cognitive Abilities.

Are internalizing and externalizing behavior problems interrelated via mutually reinforcing relationships (with each behavior leading to increases over time in levels of the other behavior) or mutually suppressing relationships (with each behavior leading to decreases over time in levels of the other behavior)? Past research on the directionality of these relationships has led to ambiguous results, particularly in adolescence. Furthermore, the extent to which prior results will generalize to adolescents with low levels of cognitive abilities remains unknown. This second limit is particularly important, given that these adolescents are known to present higher levels of externalizing and internalizing behaviors than their peers with average-to-high levels of cognitive abilities, and that the mechanisms involved in the reciprocal relationships between these two types of behaviors may differ across both populations. This study examines the directionality of the longitudinal relationships between externalizing and internalizing behavior problems as rated by teachers across three measurement waves (corresponding to Grades 8-10) in matched samples of 138 adolescents (34.78 % girls) with low levels of cognitive abilities and 556 adolescents (44.88 % girls) with average-to-high levels of cognitive abilities. The results showed that the measurement structure was fully equivalent across time periods and groups of adolescents, revealing high levels of developmental stability in both types of problems, and moderately high levels of cross-sectional associations. Levels of both internalizing and externalizing behaviors were higher among adolescents with low levels of cognitive abilities relative to those with average-to-high levels of cognitive abilities. Finally, the predictive analyses revealed negative reciprocal longitudinal relationships (i.e., mutually suppressing relationships) between externalizing and internalizing problems, a result that was replicated within samples of adolescents with low, and average-to-high levels of cognitive ability.

Neurogenic radial glia in the outer subventricular zone of human neocortex.

Neurons in the developing rodent cortex are generated from radial glial cells that function as neural stem cells. These epithelial cells line the cerebral ventricles and generate intermediate progenitor cells that migrate into the subventricular zone (SVZ) and proliferate to increase neuronal number. The developing human SVZ has a massively expanded outer region (OSVZ) thought to contribute to cortical size and complexity. However, OSVZ progenitor cell types and their contribution to neurogenesis are not well understood. Here we show that large numbers of radial glia-like cells and intermediate progenitor cells populate the human OSVZ. We find that OSVZ radial glia-like cells have a long basal process but, surprisingly, are non-epithelial as they lack contact with the ventricular surface. Using real-time imaging and clonal analysis, we demonstrate that these cells can undergo proliferative divisions and self-renewing asymmetric divisions to generate neuronal progenitor cells that can proliferate further. We also show that inhibition of Notch signalling in OSVZ progenitor cells induces their neuronal differentiation. The establishment of non-ventricular radial glia-like cells may have been a critical evolutionary advance underlying increased cortical size and complexity in the human brain.

Regulation of parkinsonian motor behaviours by optogenetic control of basal ganglia circuitry.

Neural circuits of the basal ganglia are critical for motor planning and action selection. Two parallel basal ganglia pathways have been described, and have been proposed to exert opposing influences on motor function. According to this classical model, activation of the 'direct' pathway facilitates movement and activation of the 'indirect' pathway inhibits movement. However, more recent anatomical and functional evidence has called into question the validity of this hypothesis. Because this model has never been empirically tested, the specific function of these circuits in behaving animals remains unknown. Here we report direct activation of basal ganglia circuitry in vivo, using optogenetic control of direct- and indirect-pathway medium spiny projection neurons (MSNs), achieved through Cre-dependent viral expression of channelrhodopsin-2 in the striatum of bacterial artificial chromosome transgenic mice expressing Cre recombinase under control of regulatory elements for the dopamine D1 or D2 receptor. Bilateral excitation of indirect-pathway MSNs elicited a parkinsonian state, distinguished by increased freezing, bradykinesia and decreased locomotor initiations. In contrast, activation of direct-pathway MSNs reduced freezing and increased locomotion. In a mouse model of Parkinson's disease, direct-pathway activation completely rescued deficits in freezing, bradykinesia and locomotor initiation. Taken together, our findings establish a critical role for basal ganglia circuitry in the bidirectional regulation of motor behaviour and indicate that modulation of direct-pathway circuitry may represent an effective therapeutic strategy for ameliorating parkinsonian motor deficits.

Scaling-up an efficacious school-based physical activity intervention: Study protocol for the 'Internet-based Professional Learning to help teachers support Activity in Youth' (iPLAY) cluster randomized controlled trial and scale-up implementation evaluation.

BACKGROUND: Despite the health benefits of regular physical activity, most children are insufficiently active. Schools are ideally placed to promote physical activity; however, many do not provide children with sufficient in-school activity or ensure they have the skills and motivation to be active beyond the school setting. The aim of this project is to modify, scale up and evaluate the effectiveness of an intervention previously shown to be efficacious in improving children's physical activity, fundamental movement skills and cardiorespiratory fitness. The 'Internet-based Professional Learning to help teachers support Activity in Youth' (iPLAY) study will focus largely on online delivery to enhance translational capacity. METHODS/DESIGN: The intervention will be implemented at school and teacher levels, and will include six components: (i) quality physical education and school sport, (ii) classroom movement breaks, (iii) physically active homework, (iv) active playgrounds, (v) community physical activity links and (vi) parent/caregiver engagement. Experienced physical education teachers will deliver professional learning workshops and follow-up, individualized mentoring to primary teachers (i.e., Kindergarten - Year 6). These activities will be supported by online learning and resources. Teachers will then deliver the iPLAY intervention components in their schools. We will evaluate iPLAY in two complementary studies in primary schools across New South Wales (NSW), Australia. A cluster randomized controlled trial (RCT), involving a representative sample of 20 schools within NSW (1:1 allocation at the school level to intervention and attention control conditions), will assess effectiveness and cost-effectiveness at 12 and 24 months. Students' cardiorespiratory fitness will be the primary outcome in this trial. Key secondary outcomes will include students' moderate-to-vigorous physical activity (via accelerometers), fundamental movement skill proficiency, enjoyment of physical education and sport, cognitive control, performance on standardized tests of numeracy and literacy, and cost-effectiveness. A scale-up implementation study guided by the RE-AIM framework will evaluate the reach, effectiveness, adoption, implementation, and maintenance of the intervention when delivered in 160 primary schools in urban and regional areas of NSW. DISCUSSION: This project will provide the evidence and a framework for government to guide physical activity promotion throughout NSW primary schools and a potential model for adoption in other states and countries. TRIAL REGISTRATION: Australia and New Zealand Clinical Trials Registry ( ACTRN12616000731493 ). Date of registration: June 3, 2016.