Students' cognitive and motivational profiles have a large impact on their academic careers. The development of such profiles can partly be explained by the reciprocal internal/external frame of reference model (RI/E model). The RI/E model predicts positive and negative longitudinal effects between academic self-concepts and achievements within and across 2 academic domains (i.e., the mathematics and verbal domains). In the present study, we replicated the RI/E model in 2 samples and extended it by simultaneously investigating the longitudinal associations of academic self-concepts and achievements in 3 academic domains (i.e., mathematics, German as a native language, English as a foreign language). We examined 2 domains across 4 measurement occasions in 2 independent student samples who were in Grades 5-8 (Study 1: N = 1,529) or Grades 5-7 (Study 2: N = 639). In a 3rd study, we examined a subsample of the 2nd sample (N = 465) in 3 domains. Results demonstrated support for the RI/E model for 2 as well as 3 academic domains. We found positive reciprocal effects of academic self-concepts and achievements within a domain, positive reciprocal effects between achievements across domains, negative effects of achievements on subsequent cross-domain self-concepts, negative effects of academic self-concepts on subsequent cross-domain achievements, and some support for negative effects of academic self-concepts on subsequent cross-domain self-concepts. Furthermore, we found that RI/E model effects were of comparable size across time. To conclude, the RI/E model provides significant insights into the development of distinct motivational and cognitive profiles and, thus, of becoming either a math or verbal person. Implications for research and educational practice are discussed.