Achievement motivation scores on the domain-specific level are better predictors of domain-matching scholastic performance than scores of general achievement motivation measures. Although there is research on domain-specific motivational measures, it is still unknown where this higher predictive power originates from. To address this, 715 students in secondary school answered questionnaires on general and domain-specific achievement motivation, domain-specific self-concept, and domain-specific self-esteem in two different studies. The first study was designed to disentangle the variance components in general and domain-specific achievement motivation in order to delineate hypotheses regarding potential drivers for the predictive power of domain-specific achievement motivation. The findings implied a strong role for a shared method factor. To explore the nature of this method factor, domain-specific self-concept/-esteem were focussed to establish discriminant validity evidence in a second study. The results indicate that the additional domain-specific variance can, in large parts, be explained by self-concept and self-esteem on domain-specific level.