Are there sex and grade differences in structure and levels of HEXACO-MSI-E personality traits in adolescents? A cross-sectional study

• Personality structure remains stable throughout the middle school years • H, E, A and C, with all/some facets, showed lower levels across middle school grades. • Adolescents saw their personality as developing, whereas parents as more stable. • Girls were more emotional and open, while boys were more extroverted and agreeable. • Parents reported fewer sex differences than adolescents. This paper investigated grade-related and sex differences in structure and mean levels of HEXACO traits in two samples of Italian middle-school adolescents, using self-report (N = 1707) and parental perspectives (N = 403). Results suggested that HEXACO traits are already formed by around age 10 or 11 and remain stable across middle-school grades. Compared to students in lower grades, adolescents in higher grades exhibited lower levels of Honesty-Humility, Emotionality, Agreeableness and Conscientiousness, although the lower levels of Agreeableness observed was due only to girls. Girls scored higher on self-reported Emotionality and Openness to Experience, whereas boys scored higher on Extraversion and Agreeableness. In general, facet-level analyses mirrored trait-level sex and grade differences. Finally, parents reported fewer sex differences than adolescents.