The Extent and Specificity of Relative Age Effects on Mental Health and Functioning in Early Adolescence.

Purpose: Although extensive evidence indicates that being younger within a school cohort is associated with poorer academic functioning, much less is known about such relative age effects (RAEs) for mental health--the focus of the current investigation.

Methods: Data from 23,379 11- to 13-year-olds attending state-maintained secondary schools in England were analyzed to investigate RAEs on mental health measured using the Strengths and Difficulties Questionnaire. Participants were grouped into oldest, middle, and youngest thirds of their academic year based on their month of birth relative to their cohort. Hierarchical linear regression analysis evaluated RAEs and gender- or deprivation-related moderation of such effects.

Results: Relatively younger adolescents had significantly more emotional symptoms and peer problems compared with relatively older individuals in a year group, although effect sizes were small. These effects were not moderated by gender or deprivation. Impact of mental health difficulties on other aspects of functioning was also greater among relatively younger children. Larger RAEs are observed in the younger cohort (11-12 years) compared with those in the 12- to 13-year-olds, thereby indicating that RAEs might attenuate with age.

Conclusions: Being relatively younger than classmates is associated with increased internalizing symptoms, poorer peer relationships, and higher impact of mental health difficulties on functioning at school and home. The findings support wider inclusion of relative age in understanding mental health difficulties and its inclusion as a potential risk factor in studies investigating the development of psychopathology, especially for internalizing symptoms. Possible mechanisms of the effects detected are discussed.