---
title: "Spaced repetition"
chunk: 2/3
source: "https://en.wikipedia.org/wiki/Spaced_repetition"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:26:29.414379+00:00"
instance: "kb-cron"
---

The notion that spaced repetition could be used for improving learning was first proposed in the book Psychology of Study by C. A. Mace in 1932: "Perhaps the most important discoveries are those which relate to the appropriate distribution of the periods of study... Acts of revision should be spaced in gradually increasing intervals, roughly intervals of one day, two days, four days, eight days, and so on."
In 1939, H. F. Spitzer tested the effects of a type of spaced repetition on sixth-grade students in Iowa who were learning science facts. Spitzer tested over 3600 students in Iowa and showed that spaced repetition was effective. This early work went unnoticed, and the field was relatively quiet until the late 1960s when cognitive psychologists, including Melton and Landauer and Bjork, explored manipulation of repetition timing as a means to improve recall. Around the same time, Pimsleur language courses pioneered the practical application of spaced repetition theory to language learning, and in 1973 Sebastian Leitner devised his "Leitner system", an all-purpose spaced repetition learning system based on flashcards.
With the increase in access to personal computers in the 1980s, spaced repetition began to be implemented with computer-assisted language learning software-based solutions (see § Software), enabling automated scheduling and statistic gathering, scaling to thousands of cards scheduled individually. To enable the user to reach a target level of achievement (e.g. 90% of all material correctly recalled at any given time point), the software adjusts the repetition spacing interval. Material that is hard appears more often and material that is easy less often, with difficulty defined according to the ease with which the user is able to produce a correct response.
The data behind this initial research indicated that an increasing space between rehearsals (expanding) would yield a greater percentage of accuracy at test points. Spaced repetition with expanding intervals is believed to be so effective because with each expanded interval of repetition it becomes more difficult to retrieve the information because of the time elapsed between test periods; this creates a deeper level of processing of the learned information in long-term memory at each point. Another reason that the expanding repetition model is believed to work so effectively is that the first test happens early on in the rehearsal process. The purpose of this is to increase repetition success. By having a first test that followed initial learning with a successful repetition, people are more likely to remember this successful repetition on the following tests. Although expanding retrieval is commonly associated with spaced repetition, a uniform retrieval schedule is also a form of spaced repetition procedure.
A study conducted by Bui et al. (2013) examined how the advantages of spaced repetition can be influenced by the difference in working memory and the complexity of tasks that occurs between the repetitions. The researchers found participants with a higher working memory benefited from spaced repetition and showed better performance on challenging tasks.
Spaced repetition is typically studied through the use of memorizing facts. Traditionally speaking, it has not been applied to fields that required some manipulation or thought beyond simple factual/semantic information. A more recent study has shown that spaced repetition can benefit tasks such as solving math problems. In a study conducted by Pashler, Rohrer, Cepeda, and Carpenter, participants had to learn a simple math principle in either a spaced or massed retrieval schedule. The participants given the spaced repetition learning tasks showed higher scores on a final test distributed after their final practice session.
This is unique in the sense that it shows spaced repetition can be used to not only remember simple facts or contextual data but it can also be used in fields, such as math, where manipulation and the use of particular principles or formulas (e.g. y = mx + b) is necessary. These researchers also found that it is beneficial for feedback to be applied when administering the tests. When a participant gave a wrong response, they were likely to get it correct on the following tests if the researcher gave them the correct answer after a delayed period.
Building on this, more recent studies have applied spaced repetition to procedural skill acquisition in complex domains. For example, a pilot study in neurosurgery training found that incorporating spaced repetition into a six-week simulation module improved residents’ proficiency in performing complex surgical procedures. Participants who engaged in structured, repeated practice showed significant improvements in objective performance metrics compared to those who trained using traditional methods alone. This suggests that spaced repetition can effectively facilitate the acquisition of procedural knowledge in surgical contexts, including its demonstrated applications in other areas of medical training.
Spaced repetition is a useful tool for learning that is relevant to many domains such as fact learning, mathematics, and procedural skills, and many different tasks (expanding or uniform retrieval). Many studies over the years have contributed to the use and implementation of spaced repetition, and it still remains a subject of interest for many researchers.
Over the years, techniques and tests have been formed to better patients with memory difficulties. Spaced repetition is one of these solutions to help better the patients' minds. Spaced repetition is used in many different areas of memory from remembering facts to remembering how to ride a bike to remembering past events from childhood. Recovery practice is used to see if an individual is able to recall something immediately after they have seen or studied it. Increasing recovery practice is frequently used as a technique in improving long-term memory, essentially for young children trying to learn and older individuals with memory diseases.

== Algorithms ==
There are several families of spaced repetition algorithms: