Two longitudinal extensions of the classic internal/external frame of reference model (I/EM) have attracted researchers' attention in recent years: The reciprocal I/EM (RI/EM) describes the reciprocal effects between students' math and verbal achievements and self-concepts. The 2I/EM describes the effects of students' math and verbal achievement levels and changes on their math and verbal self-concepts. The present research integrates these 2 approaches into the reciprocal 2I/EM (R2I/EM), which describes the effects of students' math and verbal achievement levels and changes on their math and verbal self-concepts and the effects of their math and verbal self-concept levels and changes on their math and verbal achievements. We tested this model in 3 empirical studies, including about 6,000 students between Grade 4 and Grade 11 from Germany, Switzerland, and Belgium, using grades and test scores as achievement indicators. Overall, we found strong support for the R2I/EM. In line with prior 2I/EM studies, students' achievement levels showed positive (negative) effects on their self-concepts within (between) subjects. The effects of students' achievement changes on their self-concepts within (between) subjects were usually positive (near 0). In line with prior RI/EM studies, students' self-concept levels showed positive (negative or near 0) effects on their achievements within (between) subjects. For the first time, we also examined the effects of students' self-concept changes on their achievements: These effects were usually positive (positive or near 0) within (between) subjects. Our findings have important theoretical and practical implications for the I/E model literature and for teachers aiming to foster their students' self-concepts and achievements.