This paper examines the effects of learning time on student achievement. It begins by reviewing what is known about how time is allocated and utilized in schools and the effects of differing amounts of exposure to schooling on achievement. Several theoretical perspectives concerning how time spent affects achievement are briefly discussed. The central focus of the paper is the development of a teacher/learner/task model of the production of learning. Incorporated into this model are three factors: task structure, nonlinear effects, and task organization. Several experiments that use this model in a computer simulation are described. These studied how variations in task structure, pacing of teaching and learning, and timing of teaching and nonteaching intervals affect achievement. The experiments suggest that different teaching strategies are required for learning tasks of different structure, that teaching strategies for producing the maximum average classroom achievement and a minimum level of competence are not the same, and that the timing of teaching and nonteaching intervals alter the effectiveness of teacher and learner. One section of the paper explains the concept of a time scale and its usefulness. A discussion and summary section containing suggestions for future research concludes the paper. (Author/JM)