The spacing effect is the phenomenon whereby learning is greater when studying is spread out over time, as opposed to studying the same amount of time in a single session. That is, it is better to use spaced presentation rather than massed presentation. Practically, this effect suggests that "cramming" (intense, last-minute studying) the night before an exam is not likely to be as effective as studying at intervals in a longer time frame. Important to note, however, is that the benefit of spaced presentations does not appear at short retention intervals, in which massed presentations tend to lead to better memory performance. This effect is a desirable difficulty; it challenges the learner but leads to better learning in the long-run.