The purpose of this study is to investigate the factors explaining differences between schools in the extent to which computers are used by subject teachers as a means of enhancing instruction and optimizing student learning. A conceptual model of key factors in educational reform and innovation is developed on the basis of theory and previous research. The parameters in this model are estimated using the linear structural relations approach and data collected for the International Association for the Evaluation of Educational Achievement (IEA) study of computers in education in two countries, Japan and the United States. The results show that, in both Japan and the United States, internal innovation assistance, teacher competence and a strategy for monitoring and problem coping are associated with the outcome variable, the degree of computer use in lower secondary schools. In Japan three other variables are also positively related to this outcome: perceptions of the school leadership concerning the relevance of computer use, whether the school has developed an explicit policy for implementation, and whether the school provides opportunities for staff development. Less variation among the predictor variables is found in the United States compared with Japan. The explanation may be that many schools in Japan are still working on the introduction of the innovation, whereas most schools in the United States have reached the stage of institutionalization.