Many sports use the academic year (1 September to 31 August) as the registration dates for entry into school, community, governing body talent pathways, and some professional competitions within the UK.
While mirroring the educational system, these specific annual-age groups provide consistency for friendship groups and continuity for youngsters, and attempt to avoid large differences between children within sport to try to ensure equal competition and opportunities.
However, this structure still leads to some children being almost one year older than others within the same annual-age group (eg a September birth compared to an August birth). This difference in age within an annual age group is defined as relative age, with the consequences being the Relative Age Effect.