Schools and sports governing bodies have added physical literacy in their curricula. However, until recently, there was no validated protocol to assess children’s physical literacy progress. In response to this need, the Canadian Assessment of Physical Literacy (CAPL) was developed; it measures physical literacy by assessing 4 important domains (physical competence, daily behaviours, motivation and confidence, and knowledge and understanding). The relative age effect (RAE) bias is attributable to age grouping by the imposition of cut-off dates; this age grouping strategy is common in sports and schools. However, despite its objective of providing age-adjusted learning, it promotes a relative age difference that leads to a developmental advantage for children born just after the cut-off date. Analogous to the age grouping in schools and sports, the CAPL protocol uses rounded-down age bands to objectively compare children; however, this type of comparison is also known for being susceptible to the RAE bias. The purpose of this thesis was to determine whether the RAE bias was associated with the CAPL scores (i.e., the four domains individually and the overall score) and all of the physical competence domain assessments individually (anthropometrics, aerobic, strength, muscular endurance, flexibility and movement skills). Participants (n=8,233, 50.2% girls), ages 8 to 12 years, from 7 provinces were tested using the CAPL protocol. Analyses of covariance (controlling for age, testing date, body mass index z-scores and testing sites) revealed a significant RAE bias in boys in 2 out of the 4 domains (physical competence and knowledge and understanding domains) and in girls in 3 out of the 4 domains (physical competence, knowledge and understanding and motivation and confidence domains). However, these significant associations between domain scores and relative age yielded negligible effect sizes, thus no meaningful RAE was observed. Collectively, the results of this thesis suggest that the RAE should not affect the validity of the CAPL in accurately measuring physical literacy.