Distributed practice refers to a schedule of learning in which practice is spread out over multiple sessions rather than concentrated in a single session ( massed practice ). Distributed practice encompasses both a spacing and a lag effect.
- Spacing effect : People are more likely to recall what they have learned if their learning sessions are spaced out than if they are massed together.
- Lag effect : People recall information better with longer lags between learning sessions than shorter lags.
The spacing effect is one of the most robust in cognitive science and was first identified by Hermann Ebbinghaus 
HE
Hermann Ebbinghaus
in his experiments on
retention
. Since Ebbinghaus, many more studies have replicated the benefits of
spaced repetition
in both children and adults. It has been demonstrated for learning simple motor skills and for learning new facts or vocabulary. However, the spacing effect has been harder to demonstrate in more complex learning tasks.
The lag effect depends on the length of the interval between learning sessions. Researchers believe that while forgetting occurs gradually over time, an additional learning session rapidly boosts the amount of knowledge retained. There appears to be a sweet spot for the time lag between learning sessions. Recall is suboptimal if the interval between sessions is either too short or too long.
… if you want to know the optimal distribution of your study time, you need to decide how long you wish to remember something.
— Nicholas CepedaNC Nicholas Cepeda and co-authors, Psychological Science
Some theorists have intuited that progressively longer gaps between learning sessions should lead to the best results, but this has not been empirically proven.
These insights imply that learners should allocate sufficient time for learning and schedule that time in a way that they can have multiple learning sessions spaced as far apart from another as possible. Because of the many variables at play (number of sessions, retention period, gap length, etc.), prescribing an optimal schedule is impossible. But a few rules of thumb should be followed:
- Spaced repetition is better than massed practice
- Longer time lags between sessions tend to yield better results than shorter ones
- The optimal gap between sessions depends on how long the knowledge needs to be retained (retention period). The longer the desired retention period, the longer the intervals should be.
- If the knowledge should be retained for periods longer than a day, the gap between sessions should be at least one day long.
- If the knowledge should be retained for months, then add a learning session after a few weeks .
- If the knowledge should be retained for years, then a learning session after a month or two should enable the best retention.
- It is better to err on the side of longer gaps than shorter ones. Shorter gaps have a more negative impact on retention than longer ones.
The key to using distributed practice is planning and time management. Start learning as early as possible and plan frequent repetitions with sufficient gaps between them. Instead of dropping things from practice too early, extend the interval between sessions and test retention again.
To efficiently promote truly long-lasting memory … very substantial temporal gaps between learning sessions should be introduced – gaps on the order of months, rather than days or weeks.
— Nicholas Cepeda
