The Korean government has initiated a nation-wide educational project that established Educational Information System (EIS) in every school and the office of education in 2003. The primary purpose of the project was to reduce teachers' administrative working loads that were the heavy burden on teachers to concentrate on their firsthand role, teaching and guiding students in school. Although it is still rare to find academic and empirical efforts and research that prove the effectiveness of the EIS, the government is trying to develop and apply a next generation EIS with an enormous budget. The purpose of this study is to identify how effectively the EIS reduced teachers' administrative working loads and thus improve their teaching ability. In order to meet the purpose this study employs descriptive methods and structure equation modeling statistics with five factors including Convenience, Usefulness, Reduction of working load, Improvement of organizational culture in decision making, Improvement of teachers' teaching ability. Consequently, this study found that teachers have a negative perception on the effectiveness of EIS. In particular, the result of the analysis confirmed that the convenience of the EIS did not directly contribute to the reduction of teachers' working loads. Meanwhile, one of the most obvious contribution of EIS on the school system was to improve transparency and reliability in the process of decision making of school.