Smiling in school yearbook photos: Gender differences from kindergarten to adulthood

To explore the hypothesis that girls and women smile more frequently than boys and men, 16,514 photographs of students (kindergarten to college) from school yearbooks were studied, as were photos of faculty and staff members. The predicted gender difference in smiling was small and nonsignificant until Grade 4, when a statistically significant difference was first obtained. The gender difference reached its peak in grade 9 (effect size = .275) and remained relatively constant through adulthood. Systematic study of yearbook photos from one high school during the period 1968-1993 revealed no change in the gender difference over time. Discussion focused on the emergence of the smiling difference during preadolescence and the theoretical implications of such a finding.