To explore the relationship between time and school learning, this paper defines the three kinds of learning time identified by researchers--allocated time, time-on-task, and academic learning time--and relates them to curriculum development. The author cites evidence that time-on-task is related to student achievement and describes two instructional approaches that have been associated with high levels of time-on-task. The first of these is mastery learning, which includes nine key elements, summarized here in checklist form. The second, direct instruction, has ten key elements and, according to the author, is similar to mastery learning. Central to both is the need for clearly defined goals, communication of expectations to students, and careful monitoring of student progress. The author lists several school districts currently involved in puttinq the research on learning time and instruction into practice and includes a capsule description of each program. Finally, implications of the learning time concept for instructional and teaching effectiveness are offered. (Author/WD)