Background: The "Relative Age Effect" (RAE) has consistently been demonstrated to influence attainment in various contexts. In education, RAE appears to provide an advantage to those born during initial months of an academic year, compared with those born in later months. A similar effect has been noted in many sports, with those born shortly after a "cut-off" date being over-represented compared to those born later in the year. Purpose: To determine if "relative age" influenced attainment in physical education (PE) as well as school sport representation in a Key Stage 3 secondary school setting. Participants and setting: For the year 2003-2004, PE attainment data and sport participation records of 621 pupils (317 male, 304 female) aged 11-14 years old, at a large secondary school in the North of England were collated and analyzed. The school contained over 1300 pupils enrolled across Key Stages 3 and 4. During 2004, the school was rated as "very good" in its educational provision by The Office for Standards in Education (OFSTED). Pupil attainment across the core subjects of English, Maths and Science was reported as similar to national averages, while the school's Physical Education (PE) provision was rated as "above the national average". Research design: The research design was cross-sectional in nature, with its goal of assessing present patterns of PE attainment and sport participation in a case-study school. Data collection: Following institutional ethical approval and school consent, annual school records relating to pupils in Key Stage 3 were collected and examined. These records documented social-demographic details including gender, date of birth as well as attainment records of the pupil. PE attainment in Key Stage 3 was based upon observational assessments by PE teachers, where mark allocations reflected the degree of pupil progress and attainment in the academic year. The school PE department was also asked to provide sport participation information. Specifically, which pupils had represented the school at least twice in the sports of soccer, rugby, netball and rounders. Data analysis: Date of birth was coded into quartiles (i.e. three-month categories) to represent relative age. A two-way between group analyses of covariance (ANCOVA) was used to examine the influence of birth date and year group on PE attainment, while Chi-square analyses examined the relationship between date of birth and school sport representation. Findings: Main effects for birth-date (i.e. quartile) and year group on attainment in PE were found as were interactions between gender and year group. Observations of school sport representation data found higher frequencies of pupils born in the first quartile were representing the school across gender and sports. Conclusions: Current age-grouping, assessment and selection strategies in school may be compounding RAEs inside and outside the classroom. School PE and sport environments may be facilitating attainment and representation for the relatively few older individuals in each year group, whilst simultaneously disaffecting a high proportion of relatively younger pupils. (Contains 2 figures.)