Background: Research across the globe has highlighted that adolescents are lacking proficiency in fundamental movement skills (FMS) and functional movement patterns, i.e. in their actual motor competence (AMC). Additionally, research in the domain of self-perceptions illustrates that adolescents possess inordinate levels of perceived motor competence (PMC) relative to their low level of actual ability. Evaluating the role of the school community (i.e. physical education class and other classroom settings) in the development of AMC and realistic self-perceptions is key, as they form essential facets to growth in these areas. This PhD research encompassed three phases. The first phase saw the gathering of cross-sectional baseline motor competence data on adolescent youth by sex and school year (i.e. grade) across the first three years (Junior Cycle) of post-primary education. The second phase formed part of a randomised controlled trial (RCT) to examine and evaluate an eight-week multi-component, school-based motor competence intervention entitled Project FLAME (Fundamental and Functional Literacy for Activity and Movement Efficiency), and its role in improving the alignment between PMC and AMC among youth. A third phase of this research comprised of a validity and reliability study to gauge the utility of a tool (utilised in phase one and two) to assess PMC data among adolescent youth. Methods: Phases one and two (baseline and RCT) recorded data among adolescents (phase one: N = 373; mean age: 14.38 ± 0.87 years; phase two: N= 324; mean age= 14.5 ± 0.88 years), in six schools (two all-male, two all-female, and two mixed-sex). In both phases, the primary outcomes measures involved 10 FMS (locomotor, object-control, and stability subsets) assessed through established measures the Test of Gross Motor Development-2 and the Get Skilled Get Active resource, in addition to 7 movements from the Functional Movement ScreenTM (FMS™). Perceived Motor competence was assessed using the Project FLAME Perceived Movement Competence Tool (PF-PMC) and the perceived functional motor competence tool. The Project FLAME intervention was structured around four components, the (i) Teacher component, (ii) Student component, (iii) Whole-School component and (iv) Digital component. Multi-level regression models were used to assess the effect of the intervention for improving the alignment between PMC and FMS. Age and sex were controlled for during these analyses, with interaction effects for the intervention and time assessed. The phase three reliability and validity study (N = 147; mean age: 13.61 ± .93 years) recruited participants from three second-level schools (one all-male, one all-female, and one mixed-sex) for a seven-day test-retest reliability assessment of the PF-PMC and concurrent validity which compared the PF-PMC with the pictorial scale of Perceived Movement Skill Competence (PMSC). Results: Results from baseline data indicated that fundamental and functional movement proficiency remained low, with high levels of self-perception not reflective of AMC. Pre-Post-intervention data following the Project FLAME intervention trial observed no significant effect for the intervention on alignment between PMC and AMC, however a small significant relationship between PMC and AMC remained (β = .23, p < .001). Phase three reported strong concurrent validity between the PF-PMC and PMSC (r = 0.83, p<.001), in addition to excellent internal consistency, and test-retest reliability. Discussion: The findings from phase one demonstrate the necessity for movement-oriented interventions in adolescent youth. Though prior research under the Project FLAME remit has previously demonstrated an ability to improve AMC in youth across 8-weeks, phase two indicates that an increase in the number of sessions may be needed to provoke greater alignment between PMC and AMC. Phase three illustrates that the PF-PMC is fit for use, though additional research for construct validity may be needed.