This randomized trial compared two types of expressive writing—benefit‐focused versus standard expressive writing—with a factual writing (control) condition in enhancing adolescents' self‐concept during the transition to high school. First‐year male students (N = 201) wrote on three consecutive days about either the potential benefits of the school transition, their deepest thoughts and feelings about this transition, or their school activities. The benefit‐focused group had better short‐term academic self‐concept relative to the other two conditions, especially among students who had low academic self‐concept at baseline, but these changes were not lasting. Writing about the benefits of the transition may be a cost‐effective school‐based intervention to strengthen academic self‐concept, but may need augmentation with booster sessions or interpersonal discussion.