The purpose of this study was to (a) test the relationships between sense of belonging to school, academic hardiness, and academic achievement and (b) examine the mediating role of academic hardiness (including commitment, control, and challenge) on the association between sense of belonging to school and academic achievement. Five hundred and twenty 15-21-year-old high school students (245 young women and 275 young men) from eight high schools in Tehran, Iran, participated in the study by completing a series of validated questionnaires. Partial least squares structural equation modeling provided evidence that commitment, control, challenge, and sense of belonging to school were positively associated with academic achievement. Commitment, control, and challenge partially mediated the relationship between sense of belonging to school and academic achievement. These findings enhance existing literature by revealing how sense of belonging to school may contribute to academic achievement.