This report summarizes and evaluates existing studies of time use in schools. The first section describes theoretical views of time and learning. Two issues are discussed: the sources of variation in learning time (actual days per school year, length of school day, absenteeism), and the effects of learning time on achievement. In the second section, a review is presented of major empirical studies of time and learning, concentrating primarily on more recent studies of the effect of time on task. An analysis is given of the results of the Beginning Teacher Evaluation Study, as well as studies of: the effect of pupil attention on achievement; the relationship between concurrent achievement and attention measures; time allocation and achievement; and student response to different teaching methods. Inconsistent effects of time variables on achievement were found in the reviewed studies, and the conclusion is drawn that the effect of time on task on learning, while important, is not substantial. The final section discusses two elements which have been given scant attention in past studies of time on task: the conditioning effect of classroom/school organizational variables, and the dynamic nature of teaching and learning. (JD)