Spacing effect

This article is about an observed effect in learning, i.e., a claim (backed by observation and experimentation) that some kinds of actions in the context of exposition, learning, practice, review, etc., on average, cause learning outcomes to move in a particular direction.
View list of observed effects in learning

Definition

The spacing effect is a term used for a related constellation of claims that learning and retention by the learner are better when the learning sessions are spaced out.

When used in the context of retrieval sessions for knowledge that has already been learned at least once, this offers a justification for the practice of spaced retrieval -- spacing out review sessions where the learner reviews/recalls/retrieves previously learned information.

When used in the context of the study of serially connected material (for instance, studying the different sections of a chapter), the spacing effect supports the idea of spacing out the study sessions, so rather than studying all sections simultaneously, the learner studies one section, spaces out a bit, then studies the next section, and so on. It also offers partial support of interleaving, though there are also other benefits of that practice.