Background: Physical literacy has been adopted in PE, sport and recreation to develop active participation in Canada. Physical literacy (PL) is the motivation, confidence, physical competence, knowledge and understanding to value and take responsibility for engagement in physical activities for life (IPLA 2015). There are three proposed domains (physical, psychological, and behavioural) for PL. Little is known about PL in children and youth. Aims: Aim 1: To characterize PL in children and youth, and to relate PL to health related fitness, performance and physical activity. Aim 2: To evaluate a PL intervention (Run Jump Throw) in grade 3/4 PE. Methods: Design: Cross-sectional (n=299, grades 3, 4, 8 and 12) and quasi-experimental intervention (n=199, 4 intervention, 4 matched comparison schools, Grade 3/4, Run Jump Throw Intervention). Instruments: Physical Literacy Assessment of Youth tools (PLAY Fun, PLAY Self, PLAY Inventory), BMI, waist circumference (WC), 20 meter shuttle run (CVFIT), sprint speed (SPEED), accelerometer measured physical activity (PA), Physical Self-Description Questionnaire (PSDQ) and the Motivation to Physical Activity Measure (MPAM). Results: Motor competence increased with grade (p<0.01). Substantial gaps (3.4% object control) in motor competence between males and females (M>F, P<0.01) identified in grade 4, the gap widens with grade (16.6% by grade 12). Motor competence was correlated (p<0.01) to -0.29 WC, -0.48 BMI, 0.54 PA, 0.56 CVFIT, 0.86 SPEED, 0.23 MPAM, and 0.5 PSDQ. The affective/cognitive domain of PLAY Self was correlated to (p<0.01) to -0.22 BMI, 0.33 PA, 0.42 PLAY Inventory, 0.46 CVFIT, 0.45 SPEED, 0.44 MPAM, and 0.79 PSDQ. Moderate associations were observed between physical and psychological domains of physical literacy. PLAY Self demonstrated convergent validity with PSDQ and MPAM. The Run Jump Throw intervention improved motor competence (5.5%, p<0.01), and was greater than comparison schools (3.5%, p<0.05). Conclusion: Physical literacy shows appropriate linkages to health related outcomes in two key domains, physical and psychological. The gender gap in physical literacy is alarming, and requires studies for remediation. These results support the notion that PL may be a gateway to physical activity in youth, and that PL can be enhanced by means of quality PL enriched lesson plans in schools. / February 2017