Description: The Taiwanese 8th graders' data of TIMSS 1999 analyzed via the structural equation modeling (SEM) technique (Chien, Jen & Chang (submitted)) confirmed Marsh's Internal/External frame of reference model (I/E model) but didn't completely agree with Marsh and Koller's (2004) Unification model. The I/E model demonstrates the effects of one's achievement in various subjects (e.g. math and verbal) on academic self-concept, and the Unification model provides a statistical framework to illustrate the reciprocal causality between academic self-conception and achievement. This study aims to examine the two models from developmental and cultural perspectives. The research questions include: 1. Whether the causal relations of academic self-conception and achievement in science and math are the same for both Taiwanese 4th and 8th graders? 2. Whether the causal relations of academic self-conception and achievement in science and math are same for the students from different cultural countries? Released TIMSS 2003 data for Taiwanese 4th and 8th graders will be explored by using the SEM method to address the first question; and four countries' data (USA, England, Taiwan and Japan) will be investigated to address the second one. Six indices (GFI, RMSEA, NNFI, CFI, PGFI and CN) will be tested for examining the fitness of each model.