Reports on population movement(2000-2030) by the National Statistical Office show that the number of elementary school age population will be decreased by 1.4million from 2005 to 2020. It will effect both school size and the policies for school facilities, which have focused on downsizing class as the high standard of OECD nations. As the unfolding evidence is emerging that a number of schools and classes will be emptied out by 2030. This study aims at developing a model for evaluating the validity of school establishment, which would help more reasonable decision-making for new school construction and the class extension in the existing schools. It classifies two different ways in founding a new school - school establishment in a residential developing site and school establishment for solving a overcrowd class. It proposes the assesment items and the methods for evaluating its validity. In the end, it suggests an assesment model which the district educational offices can use in the course of planning the student accomodations to schools and making decisions for new school construction and the class extension in the existing schools. This study would be expected to help the reasonable expenditure for school facilities and to restrict overbuilding of surplus classes.