In this research, we observed how students perform as they followed the teachers`` instruction, and consequently perform their realized potential. As the accountability of school education is emphasized, various attempts try to disconnect the vicious cycle of producing low achievers. Efforts are allocated into developing a method to minimize cumulative effect of the lag in educational benefit by focusing on the elementary education. Based on the 2007 revised curriculum, mathematics achievement level and assessment criteria were developed. These criteria were used to standardize the course and assessment objectives for 4th through 6th grade students`` mathematics studies, and to assess lower performing students and the lag in their mathematical understanding. The educational materials and assessment criteria can be expected to lead lower performing students by giving them the personalized lesson plans to minimize the lag of mathematical understanding, and eventually expedite their progress and prevent cumulative effect of the lag in the following curriculum.