Two lines of research have emerged to study the causes and prevention of student failure in virtual (K-12) schools: studies of learner characteristics and studies of learning environment characteristics. To develop a useful model for predicting failure and promoting success in virtual school environments, a study was designed to measure the relation between a combination of student and environmental factors derived from previous research and successful course completion during one semester at a large (N = 4,100) virtual school. Study findings yielded a model that can discriminate between successful and unsuccessful online school students and is especially effective at identifying those likely to succeed. (Contains 5 tables.)