This study investigated sex differences in goal orientation during adolescence. 910 adolescents aged 10-19. years read vignettes of students reflecting four goal orientations and indicated which student they resembled most. Boys and girls from two age-groups (10-14 versus 14-19. years old) were compared. Multinomial logistic regression was performed with goal orientation as dependent variable, including level of parental education as a covariate. Results showed that girls were more likely than boys to endorse mastery goals (48% vs 39%) or performance-avoidant goals (20% vs 14%). Boys more often endorsed work-avoidant or performance-approach goals. At age 14-19. years, work-avoidance was more than twice as common for boys as girls (27% vs 12%). With age, mastery goals decreased (from 52% to 36%), whereas work-avoidant goals increased (from 8% to 18%). These age and sex differences in goal orientations may be a possible explanation for boys' lower academic achievement compared to girls' and show a need for early intervention. © 2012 Elsevier Inc.