Nist and Joseph (2008) have confirmed earlier research showing that adding and interspersing a large number of time-consuming learning trials targeting known items (e.g., incremental rehearsal (IR) or interspersal) retards student learning rates. In addition, their current study has confirmed earlier research that adding and interspersing known items can improve the quality of learning trials, or the amount learned per unknown-word trials. Although the author has stressed learning rates, the Nist and Joseph finding that adding and folding in unknown items enhanced learning levels is important. The author contends that if one can determine why IR caused increases in learning levels (not rates), educators and researchers may be able to develop strategies that allow them to strengthen the effect (e.g., cause larger learning level increases) and/or make the application of the procedure more efficient (e.g., take less instructional time). Thus, these findings may lead to the development of strategies that can then be applied to enhance rather than retard learning rates. (Contains 1 table.)