Research evaluating the variables that influence learning has devoted inadequate attention to the influence of the amount of new material presented at one time. The current study evaluated the impact of varying instructional set size (ISS) on the rate at which elementary school students mastered multiplication facts while receiving constant time delay (CTD) instruction. Instructional time was equated across conditions. Instruction was provided for an ISS of five and 20 using CTD instruction for multiplication facts. ISS 20 was more efficient for two out of the three participants. This suggests a much larger efficient ISS than previous research. The implications of this finding for the importance of the instructional method in attempting to identify an efficient ISS, as well as the study's connection to prior research, in this area are discussed.