Educational theorists and researchers have long considered time a key component of individual learning. Caroll, in his classic model of school-based learning, conceptualized achievement as an outcome of two time variables: first, the amount of time a learner is engaged in learning; and second, an individual's learning rate. Caroll's ideas generated a wave of research on instructional time and learning. Many studies focused on issues of classroom dynamics and teaching efficiency; others were preoccupied with establishing statistical associations between time variables and pupil achievement. Overall, evidence from various studies suggests that there is a positive--and fairly consistent--association between instructional time and pupil achievement. Researchers disagree over the magnitude of this relationship, the relative importance of various intervening factors, and the nature of the socio-economic contexts in which the relationship is more or less salient. In this article, the authors assess the implications of these issues in the educational settings of the least-developed countries (LDCs), and briefly discuss key distinctions with respect to instructional time. (Contains 15 notes.)