Although many studies have shown the impact of comparisons on academic self-concepts, no interventions have specifically targeted comparison processes to enhance students' self-concepts. To address this gap, we developed three intervention modules aiming at increasing students' math or German self-concepts through social, dimensional, or temporal comparisons, along with beliefs related to these comparisons. The comparison-related beliefs were students' belief that classroom comparisons lead to a nonrealistic self-concept (social comparison-related belief), their belief in the interdependence of math and verbal abilities (dimensional comparison-related belief), and their belief in the changeability of abilities (temporal comparison-related belief). Each module focused on one type of comparison and a related belief. We conducted an evaluation study with N = 857 students from Grades 9 and 10, randomly assigned to either a comparison module (math or German) or a mindfulness control group. Latent change score models showed that students in the social, dimensional, and temporal comparison modules in math experienced a greater increase in math self-concept and in comparison-related beliefs than those in the control group, while no significant changes were observed for German self-concepts and only a few significant effects for the comparison-related beliefs in German by students in the comparison modules in German. Furthermore, changes in dimensional and temporal comparison-related beliefs correlated positively with changes in self-concepts, while changes in the social comparison-related beliefs did not correlate with self-concept changes. These findings provide valuable insights into the psychological mechanisms of comparison processes and suggest a novel approach to enhancing students' math self-concept.