Now, school effectiveness is a becoming an extremely important concern for educational reform policy in every nations. In Korea, however, in both government and educational organizations, the theoretic and systemic study on school effectiveness has not done yet. Although the concept of school effectiveness is important to both the theory and practice in the field of educational administration, and although effectiveness studies in educational administration focus on everything from the job satisfaction of teachers to the equity of polices on student discipline, the studies to clarify the criteria or determinant factors for the school effectiveness based on given educational conditions has been rare. In this study, my purpose is to explore what factors can be applied and appropriated to determine school effectiveness at the elementary and secondary school level in the context of school improvement in Korea. In order to explore determinant factors of school effectiveness, it is essential to establish effectiveness criteria in school. Therefore, on the basis of a survey of the theoretical background and literature concerned, and from the analysis through explorative procedures, serveral determinant factors are suitable for our eductional conditions were identified as follows; 1. principal's instructional leadership, 2. teacher's instructional behavior, 3. academic emphasis:clear goal and standard, 4. maximized learning time-on-task, 5. teacher's high expectations for the student, 6. classroom orderliness and student discipline, 7. curriculum articulation and coordination, 8. opportunities for meaningful student participation and sense of responsibility, 9. teacher commitment, 10. parental involvement. The following conclusions can be drown. That is, the school social system, in this study, is defined as the norms, beliefs and attitudes reflected in institutional patterns and behavioral practices enhance or impede school effectiveness and student academic achievement. Principal's instructional leadership is shown to be more influential factors to improve school effectiveness and school learning climate can be have more direct effect on school effectiveness through school social system. Behaviors of members in school, especially student outcomes in academic subject is partly a function of the cultural and organizational characteristics of school. In effective school, there are clearly defined official goals concerning student's basic skill acquisition, and usually successful principals were actively involved in setting instructional goals and developing performance standards for student.