Research has found that factors such as content, prompts, and individual motivational differences affect instructional effectiveness. While instructional effectiveness is acritical outcome variable, the limited availability of instructional time results in instructional efficiency being acritical consideration. This study evaluated whether varying instructional set sizes (i.e. the number of unknown items taught within a specified period of time) produced differential learning. Instruction was provided on arbitrary number-word relationships. Response to learning sets was studied using a within-participants experimental design. This study differs from prior research by examining set size for the commonly used constant time delay procedure. The results suggested that, for the majority of students, learning five novel items at a time was less efficient than one of the larger sets of unknown items. Additionally, participants demonstrated individual differences in learning rates. The implications of these findings for instructional presentation and intervention efficiency are discussed.