What is the Optimal Spacing for Review?

Continuous learning encompasses a number of learning strategies, one of which is spaced review after the completion of a course. This review can be in the form of adaptive questioning exercises, subscription-based micro-lessons, or some combination of the two.

Which raises a question: For long term retention what is the optimal period of spacing for the review? Or put another way:

How long after learning is completed should learning review take place?

The Answer: There is probably no single answer to that question — a lot depends on the material and the learners — but in one study three researchers (Irina Kapler, Tina Weston, Melody Wiseheart) compared a one day review delay (before forgetting sets in) to an eight day delay. Which do you think is the more optimal delay? And does it matter if they are testing lower level or higher level reasoning?

In their article “Spacing in a simulated undergraduate classroom: Long-term benefits for factual and higher-level learning.” (Learning and Instruction 36 (2015) 38-45) they present the results of the following study:

The researchers presented a 45 minute lecture to 169 learners then split the learners into two groups: one group reviewed the material after one day, the second reviewed after eight days. They then tested both groups on the material after 35 days.  They tested the groups on simple factual recall (Knowledge level of Bloom’s Taxonomy) and higher level questions (Application level of Bloom’s Taxonomy). The results were:



In both cases an eight day delay for review is better than a one day delay.

This study only looks at two data points (one day and eight days) so it doesn’t answer the question of the optimal spacing (it could be five or ten, or as mentioned above – it could depend) but other studies have suggested that it is best to review after some forgetting has set in.


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