Background: The internal/external frame of reference (I/E) model by Marsh (1986) assumes intra-individual dimensional comparisons in which students compare their own achievements in one subject with their achievements in other subjects. These comparison processes should lead to negative paths from achievement in one subject (e.g. maths) on self-concept in another subject (e.g. verbal domains). Aims: Within this study, we investigated the impact of students' belief in a negative interdependence of maths and verbal abilities, that is, whether students think of maths and verbal abilities as negatively correlated or not, on the impact of dimensional comparisons. Methods: Maths and German grades, academic self-concepts in maths and German, and a new scale on the beliefs in a negative interdependence of maths and verbal abilities students were assessed (N = 1,443). Results: The importance of the negative interdependence beliefs could be shown: stronger belief in a negative interdependence of maths and verbal ability are accompanied by more negative path coefficients from grades in one subject to academic self-concepts in the other subject. Conclusions: Dimensional comparisons seem to be of particular importance for students with negative interdependence beliefs.