The present study investigated the effectiveness of two short relevance interventions (writing a text or evaluating quotations about the utility of mathematics) using a sample of 1,916 students in 82 math classrooms in a cluster randomized controlled experiment. Short-term and sustained effects (6 weeks and 5 months after the intervention) of the two intervention conditions on students' competence beliefs (self-concept, homework self-efficacy), teacher-rated individual effort, and standardized test scores in mathematics were assessed. Hierarchical linear regression analyses showed that students' homework self-efficacy was higher in both intervention groups 6 weeks and 5 months after the intervention compared to the control condition. Students' self-concept, teacher-rated effort, and achievement in mathematics were promoted through the quotations condition, partly in the long term.