Background: The reciprocal I/E model (RI/EM) combines the internal/external frame of reference model (I/EM) with the reciprocal effects model (REM). The RI/EM extends the I/EM longitudinally and the REM across domains. The model predicts that, within domains, mathematics and verbal achievement (VACH) and academic self-concept have positive effects on subsequent mathematics and VACH and academic self-concept within domains but have negative effects across domains. Aims: The main purpose is to validate the RI/EM and extend it using objective achievement indicators and grades. Sample: Two waves of data collection from grade 5 to grade 9 with N = 1,045 secondary school students were used. Methods: Test scores, grades, and self-concept data were obtained. The main analyses were conducted using hierarchical linear modelling. Results: The positive longitudinal effects of grades and test scores on subsequent grades, test scores and academic self-concept within domains and the negative effects of grades and test scores on subsequent academic self-concept across domains supported the RI/EM. The effects of academic self-concept on subsequent grades and test scores across domains were near zero when prior achievement indicators were controlled for. Overall, the results using school grades as achievement measures were replicated using standardized achievement test scores. Conclusions: The results serve to highlight the importance of the combination of common theories, which are mostly investigated individually, to enhance our understanding of the complexity of within- and across-domain relations between academic self-concepts and achievement using grades as well as test scores.