Although the spacing effect has been studied extensively and has been proven to improve individuals’ learning capabilities, it is still not widespread in schooling systems. Schools do encourage study habits that align with the spacing effect, but not to the extent that many experts recommend. 

However, let’s not be too quick to blame educators for not optimizing the spacing effect in classrooms. First, finding the optimal spacing interval can be challenging. If presentations or tests are too widely spaced, students will forget the material and need to relearn it. Equally, if tests are not spaced enough, testing will not require sufficient mental effort to produce the desired effects on memory (the harder it is to recall something, the better we later remember it). A good example of this conundrum is flashcards. When used in quick succession, they can result in improved short-term retention, but in the long term, there is no effect. Students tend to use flashcards in relatively close succession, so there is not enough spacing between retrieval attempts.⁴ Another critical consideration for educators is finding just the correct number of repetitions necessary to retain information over long periods. As you can imagine, experimenting with spacing and number of repetitions is not easy in busy schools where time is already limited. 

Corporations can also use the spacing effect to capitalize on and improve the returns on their advertisements and marketing efforts. According to American venture capitalist and entrepreneur Garry Tan, startups that have just launched should get in front of their audience again at 2, 7, 30, and 60 days later to have the most significant impact. When it comes to promoting a new product or service, companies will optimally space advertisements so that individuals can better remember their offerings. We remember ads that are strategically placed and spaced out, even though their products might not be the best or most reliable.3 Following this logic, companies will avoid placing ads one after the other throughout a television program, but rather spaced apart, leading us to remember the products better than we would initially. 

By failing to incorporate the spacing effect in school systems globally, the education system is missing a pivotal opportunity to teach students how to learn effectively.¹ Cramming techniques, which are popular among students, are tedious and ineffective and do not lead to long-term learning. By leveraging the spacing effect and its close cousins, the lag effect and testing effect, education systems can be strengthened, and learning outcomes improved. 

Yet it’s not only in the traditional classroom where the spacing effect can be used to improve education systems and strategies. Companies, businesses, and organizations can use the spacing effect to enhance their training and onboarding programmes, making them more efficient and memorable. By spacing out training sessions and incorporating well-placed follow-up content, organizations can improve employees’ retention of important information and ultimately enhance workplace performance. 

Years of research on memory and our ability to recall information have led to many theories for why the spacing effect occurs. Other potential reasons for the spacing effect include the following:

Forgetting and Learning are Linked

When individuals review close to the point of nearly forgetting, our brains reinforce the memory and add new details. This is why teaching others and writing practice papers are effective ways for students to revise and highlight what’s been forgotten in their own learning.¹

Retrieving Memories Changes the Way They are Later Encoded 

Practice tests are an effective method of studying because of their level of difficulty. Difficulty makes individuals recall information instead of just recognizing it when studying. The harder it is to remember a piece of information while practicing it, the better it will be retained or recalled later. The more strain it takes to remember information initially, the more mental labor an individual causes themselves, resulting in the action of recalling being more natural in the future.¹

Great Importance Assigned to Repeated Information 

The information an individual encounters regularly becomes effortless to recognize in the future. An example of this includes an individual’s telephone number, directions to work, or names of coworkers. Though occasionally an individual may forget these things, because they are repeated so often, they are typically easy for individuals to access and remember. 

Semantic Priming

The associations people form between words have also been speculated to impact the spacing effect. Semantic priming describes why it’s easier to remember words or sentences linked or connected to one another. For example, the sentence “the nurse and the doctor go to the hospital,” is easier to remember than “the artist and the driver go to the supermarket”. This is because, in the first sentence, nurse, doctor, and hospital are linked, making it easier to remember. It’s also been theorized that repetition over time primes individuals to make connections to information or words in sentences.¹

Individuals can use the spacing effect effectively to learn and retain information better. Improving our memory and learning throughout our life can greatly help us succeed. By capitalizing on the cognitive benefits of the spacing effect, and incorporating effective learning processes, we can better ourselves, our decision-making abilities, and our learning capabilities. Likewise, schools, businesses, and organizations can leverage the spacing effect to support their students and employees to better retain and recall important information. 

The spacing effect even has an impact on our bodies at a cellular level. A study conducted by Helene Sisti, Arnold Glass, and Tracy Shors explored the spacing effect with respect to its effect on learning and neurogenesis (the formation of new neurons in the brain) in the dentate gyrus of the hippocampus region of our brains.⁵ The hippocampus is essential for learning and memory, with thousands of new neurons generated daily. However, many of these cells die within a few weeks. The researchers conducted two experiments where they trained animals with spaced and massed trials to complete the Morris water maze, a test for spatial learning commonly used with rodents. The animals trained with spaced trials performed as well as those trained with massed trials but could remember the location better two weeks later and retained a higher proportion of cells. The researchers concluded that learning over time through spaced training enhances memory and improves the survival of new neurons in the brain. 

However, just as important as the spacing effect is how we research and study the phenomena. While many advocates of the spacing effect may say that simple spaced presentations of information in classroom settings will enhance students’ retention of information, the reality is far more complicated. We also need to be aware of what Delaney et al. call “imposter” effects, such as rehearsal borrowing, strategy changes during the study, recency effects, and item skipping, all of which can complicate the interpretation of spacing experiments. The difficulty of the material being learnt also impacts the spacing effect, with more challenging content requiring different spacing strategies to easier information. To overcome these interferences, the authors suggest standardizing spacing intervals across studies, testing a wider variety of materials beyond simple word pairs and vocabulary items, and looking at how the spacing effect operates across different learning types and content.  

By being aware of the spacing effect, individuals can use it to their advantage. By effectively utilizing the spacing effect to better ourselves for work or school, we can take advantage of this cognitive effect and improve our daily lives. The spacing effect can be activated in the following ways: 

Schedule Information Review 

The act of scheduling period for information reviews, typically follows a hierarchy review process, such as going over information after an hour, a day, then every other day, weekly, monthly, and so on. By planning and scheduling these reviewing sessions, you can enforce the spacing effect into your learning habits and process.

Store and Organize Information

The use of flashcards, or spaced repetition software such as Anki and SuperMemo, are standard tools to help individual’s practice integrating the spacing effect in their learning. Softwares like those mentioned above aid in providing a schedule for individual’s to follow and give the advantage of requiring little effort on the individual’s part to maintain.

Create a Metric for Tracking Progress

Additionally, space repetition techniques and systems have been found to work best when including forms of positive reinforcement. Applications like Duolingo incorporate positive reinforcement in their learning processes, by similarly using a points system to motivate users to practice languages and improve continuously. Tracking progress can give individuals a sense of improvement and achievement, motivating them to continue learning.

Create Set Durations for Review Processes

Finally, limiting our practicing time is essential when using the spacing effect. When individuals practice for too long, their attention spans are likely to waver, resulting in a decreased amount of retained information. A typical recommendation for learning sessions is 30 minutes long, with breaks to split up these sessions.¹

If you were hoping to learn exactly how long proper spacing is from this article, you might be disappointed. Although studies have shown that longer spacing intervals produce better retention, a definitive optimum gap cannot be determined.⁶ This is because memory and learning are highly subjective processes influenced by the difficulty of the content, individual variations, and other cognitive biases.

The spacing effect has been referred to as one of the oldest and best-documented phenomena in the history of learning and memory research.¹ The spacing effect was first identified by German psychologist Herman Ebbinghaus, a pioneer in quantitative memory research, with his most important findings in forgetting and learning curves.¹ Ebbinghaus first detailed the phenomena in 1885 in his book Memory: A Contribution to Experimental Psychology, in which he explained that individuals forget 80% of newly learned information within 24 hours.¹

But how did Ebbinghaus make this profound discovery? To investigate memory processes, Ebbinghaus subjected himself to numerous trials where he would attempt to learn and recall lists of these nonsense syllables. He meticulously controlled different variables, such as the study time, intervals between sessions, and repetitions, in order to systematically investigate the effects of repetition and timing on memory retention. To eliminate the effect of pre-existing associations with words or phrases, he created 2,300 “nonsense syllables”—combinations of a consonant, a vowel, and a consonant (e.g., “VUD” or “ZOF”)—that he would memorize in various sequences and attempt to recall. Ebbinghaus conducted numerous trials in which he memorized and attempted to recall lists of these syllables, varying the study time, intervals between sessions, and repetitions. Through these self-experiments, he measured forgetting over time, coining what is known as the “forgetting curve” by analyzing how many repetitions it took to relearn lists after various intervals. 

Overall, Ebbinghaus observed that lists learned with spaced-out sessions required fewer repetitions for relearning than those learned in one concentrated effort, demonstrating that distributed practice enhances long-term retention. Ebbinghaus also introduced the “savings” method, which measured how much faster he could relearn previously studied material compared to learning it for the first time, providing insight into memory decay and implicit memory.⁷ 

12 years later, in 1897, fellow German psychologist Adolph Jost incorporated the advantage of spaced practice over massed practice into his laws of memory and forgetting. More specifically, he stated that if two memory traces have the same strength, then two things will occur: first, repetition of the older trace will strengthen it more than repetition of the newer trace, and second, the older trace will deteriorate less quickly than the newer trace.⁷ 

Since Ebbinghaus’ groundbreaking discovery,  researchers have explored some of the key mechanisms behind the spacing effect and under what conditions it occurs. In 1973, Douglas Hintzman and Richard Block proposed the concept of ‘study-phase retrieval’ which refers to recognizing that something is repeated when you see it.⁸ The authors argue that in order for the spacing effect to work, an individual must retrieve the prior presentation (thus assuming that they realize the information is repeated). The study-phase retrieval accounts for the lag effect U-curve because as the spacing between repetitions increases, it becomes harder to remember the original presentation of the information. Similarly, if the previous repetition of the information is not retrieved at all, there is no benefit of the spacing effect at all. 

Alongside the study-phase retrieval concept, one of the most influential mechanisms proposed to account for the benefits of the spacing effect is encoding variability. First researched by Arthur Melton and later Robert Bjork in the 1960s and 70s, encoding variability describes how information is encoded in memory more effectively when it is learned in different contexts or at different times (as opposed to massed repetitions). When learning is spaced out, it allows the learner to encounter the information in various contexts, including different environments or emotional states. This variability is key to the encoding process because it creates multiple retrieval paths for the same information, making it more accessible later. Likewise, when information is learned close together (massed repetitions), they can interfere with each other. In contrast, learning information in varied contexts or at spaced intervals can help better distinguish items and enhance recall. 

Finally, in 1989, cognitive psychologist Robert L. Greene combined study-phase retrieval with deficient processing to create a two-factor account of the spacing effect. Greene suggested that when information is studied in a massed format (e.g., cramming), attention and cognitive processing diminish because the material is repeatedly encountered without sufficient intervals. This deficient processing leads to shallow encoding, making the information harder to retain over the long term. According to his theory, spaced practice forces a more effortful retrieval process which strengthens our memory of material. 

You may be asking, can all of these mechanisms really contribute to the spacing effect? Because this phenomenon occurs under such a wide variety of conditions, it's proved difficult to develop a consistent mechanistic account of why it happens.

As we saw earlier, working out the optimum spacing between, and number of, repetitions for improved learning can be a significant challenge. Luckily, AI-driven educational technologies can help teachers and other educators integrate the spacing effect into their students’ learning and revision regimes without spending hours conducting laborious self-experiments like our poor friend Ebbinghaus. 

Leveraging AI to optimize learning schedules allows for the personalized implementation of spaced repetition, where algorithms can assess a user’s progress, retention rates, and difficulty with specific material to deliver content at optimal intervals. This dynamic approach enables AI systems to “predict” the best time for each learner to review information, enhancing long-term retention and engagement. Additionally, AI-powered spaced repetition systems can adapt in real time, refining intervals as the learner’s memory strengthens or weakens over time, which is particularly beneficial in e-learning and language acquisition platforms. A famous example of these capabilities in action is Duolingo, the popular language learning platform. Duolingo uses machine learning algorithms to optimize review sessions based on each user’s progress and retention patterns. For example, if a learner struggles with specific vocabulary or grammar, Duolingo’s AI schedules those items to reappear at optimal intervals, aligning with the spacing effect to help reinforce memory and improve long-term retention.

The effects of spacing are perhaps most notable in education and learning. Though it is commonly accepted that the spacing effect and repetition produce significant learning gains for individuals, most textbooks are written in discrete chapters, which do not enforce repetition of the subject throughout. To test an alternative, in 2006, Dr. Rohrer created a two-part study where sets of students were taught how to solve math problems.¹

In the first part of the experiment, students either used massed or spaced practice to study and solve the math problems. Massed practice in references to studying is typically referred to as “cramming,” where individuals study intensively to absorb mass amounts of volumes of information in a short period of time.8 The study found that students using spaced studying practices showed significant improvements over massed studying practices when tested a week into the study.

In the second part of the experiment, the math practice problems were grouped by either type or mixed randomly. Students who had solved and studied using randomly mixed problems were significantly superior to students who had solved and practiced problems that were organized by type. Researchers attributed these results to the fact that students who practiced with type organized questions, knew the formula for solving equations in practice, but not necessarily when to apply the formula when questions were mixed. By mixing these problems across several chapters in textbooks, students would both learn the formula and when to appropriately use each formula. Similarly, courses that have cumulative final exams are believed to promote long-term retention, as it forces spaced-learning to occur throughout the semester.¹

Another example of spaced learning in education can be seen in a study on human memory for word lists conducted by developmental psychologist Lorraine Bahrick in 1993. In a nine-year-long study, four different English-speaking subjects were asked to learn 300 words in a foreign language. Participants were given several training sessions conducted in spaced-out intervals over several days and then tested for their retention through verbal recall tasks. The study found that having thirteen training sessions spaced across 56 days was equivalent to having 26 training sessions across 14 days, demonstrating the result of spaced learning, and the potential benefits if implemented in more mainstream learning practices.³

The spacing effect has many applications in the business world, specifically in regards to marketing and advertising. For example, the spacing effect indicates that for a customer to remember an advertisement better, it would be recommended for the advertisement to be spaced out and not play the same commercial back-to-back on the television, or in other forms of media.

Researchers have concluded the assumption that spaced out ads are remembered better than ads repeated back to back.¹² Additionally, advertisements with layout variation have an impact on converted sales. When studying website advertisements, researchers found that sales diminished if customers consistently visited the same website and were exposed to the same ad several times. In turn, if more time elapsed between website visits, the same presented advertisement had a more substantial effect on sales and positive conversions on the website.¹¹

What it is

The spacing effect aids individuals in better remembering and learning information. The spacing effect occurs when an individual repeats information over a spaced-out time, resulting in better recalling and retaining the information. 

Why it happens

The spacing effect is theorized to occur for a multitude of reasons. Popular speculated reasons for the spacing effect include concepts like how memories are encoded when we retrieve them, how repetition aids in remembering, and finally, the effects of Semantic Priming on recalling information. 

Example 1 – Studying

The spacing effect is commonly seen in cases of education and learning. In 2006, Dr.Rohrer created a two-part study where sets of students were taught how to solve different sets of math problems. Those who used the spacing effect to study completed the math equations and performed significantly better than students who used the massed study techniques.

Example 2 – Advertising

Examples of the spacing effect are also notable in marketing and advertising. Companies can better create memorable ads and products, by airing advertisements that are spaced apart over a more extended period of time, instead of ads that are seen or aired back to back. Ads that utilize the spacing effect to their advantage remembered better than their counterparts.

How to activate it

We can incorporate the spacing effect in our day to day, to promote better learning and decision-making abilities. The spacing effect can be activated by: scheduling spaced-out review periods, storing and organizing information by using applications such as Anki, SuperMemo or handmade flashcards, tracking progress, and reviewing in 30-minute intervals with breaks.

Why do we remember information that we attach significance to better than information we repeat?

The way in which information is encoded affects how well it is remembered and recalled. The levels of processing model challenges the idea that mere repetition of something helps us to retain it in the long term. This article looks at the model in detail, exploring why it happens and why it is important to our everyday lives.

Why Most Training Fails and How to Make Yours Work

The spacing effect can help improve training and upskilling outcomes, but what else can you do to ensure that your teams are getting the best out of their development opportunities? Dr. Maraki Kebede explores what effective training looks like, providing actionable and real-life examples to help achieve realistic training goals.