The amount of instruction students receive has long been viewed as a foundational educational resource. This article presents an analysis of the time students spend in elementary English language arts (ELA) and mathematics instruction. In mathematics, the average student received about 140 hr of instruction, but students in the top sixth of classrooms in this distribution can expect to receive between 80 and 160 hr more instruction over the school year than students assigned to the bottom sixth of classrooms. We found similar magnitudes of variation in ELA. Although most of the variation was due to differences among classrooms, there was also substantial variation among schools. Some variation in instructional time is expected and probably favorable. However, we argue that the large variation demonstrated by these results represent substantial inequity in students' opportunity to learn ELA and mathematics. (Contains 3 notes, 4 figures and 13 tables.)