“Spacing Learning Events Over Time: What the Research Says”, 2006-02 (; backlinks):
This report reviews research on the spacing effect and related learning factors from the preeminent refereed journals on learning, memory, and instruction.
The research shows that spacing learning over time produces substantial learning benefits. These benefits result from different mechanisms, including those based on repetitions and those based on other factors. Spaced-repetition effects are particularly noteworthy given the enormous research literature supporting their use. The following findings are highlighted in the report:
Repetitions—if well designed—are very effective in supporting learning.
Spaced repetitions are generally more effective than non-spaced repetitions.
Both presentations of learning material and retrieval practice opportunities produce benefits when used as spaced repetitions.
Spacing is particularly beneficial if long-term retention is the goal—as is true of most training situations. Spacing helps minimize forgetting.
Wider spacings are generally more effective than narrower spacings, although there may be a point where spacings that are too wide are counterproductive. A good heuristic is to aim for having the length of the spacing interval be equal to the retention interval.
Spacing repetitions over time can hurt retrieval during learning events while it generates better remembering in the future (after the learning events).
Gradually expanding the length of spacings can create benefits, but these benefits generally do not outperform consistent spacing intervals.
One way to use spacing is to change the definition of a learning event to include the connotation that learning takes place over time—real learning doesn’t usually occur in one-time events.