Marsh and Koller (2004) combined the reciprocal-effects model and the internal/external frame-of-reference model into a unified model of relationships between academic self-concept and achievement. However, this model has only been examined with German adolescents. We decided to test this model with two-wave data drawn from a national survey of Taiwanese students. We found that reciprocal effects exist for both math and Chinese for the high-school students. However, the causal relationship of academic self-concepts and achievement for pre-adolescents seems to vary depending on school subject. Moreover, the causal effects from academic achievement decline with age, whereas those from academic self-concepts increase with age, suggesting a developmental trend. The negative cross-domain effect from prior achievement to subsequent academic self-concept is not strong in the unified model. (Contains 2 tables and 3 figures.)