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Spacing, Testing, and Feedback: Helping Students Overcome Forgetting

How can students’ forgetting be reduced? The spacing effect – a promising strategy from the field of cognitive psychology – might hold some of the answers. Research has demonstrated that information is remembered two to three times better if study sessions are spaced in time rather than massed together. The testing effect is another research-based teaching strategy that is often used in conjunction with spacing to minimize forgetting. Actively recalling information from memory is a harder task than simply re-reading or listening to the information again. This forceful retrieval process aids in strengthening the memory trace, leading to deeper, more meaningful encoding. Finally, providing timely feedback after an incorrect response increases students’ performance during the learning session and leads to a significant increase in long-term retention.

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“I forgot.” 

“I think we learned it last year, but …”

As educators, how many times have we heard these excuses? Students forget a lot of what they’ve learned. That’s a fact.

The phenomenon of forgetting – and how to prevent it – has been a hot research topic in psychology for over 100 years. A study from the 1920s demonstrated that two thirds of knowledge successfully remembered by students at the end of a course is forgotten just eight weeks later.[1]Most knowledge does not even last until a final exam; we forget up to 60 percent of learned information just an hour after learning takes place.[2] Furthermore, if the information being learned is counterintuitive – such as the fact that the wood on the back of a violin is the primary source of sound, rather than the strings – only 10 percent of that counterintuitive information is retained a mere 15 minutes after learning.[3]

For many courses, especially those that are cumulative in nature like math and science, forgetting old content makes teaching new content difficult. These courses involve increasingly abstract skills and require students to have a solid knowledge base in order to be successful in later grades. Students really do have to master the multiplication table and the periodic table at an early age in order to move on to more complex problem solving in algebra and chemistry courses.

To compensate for high rates of forgetting from grade to grade, teachers spend valuable class time re-teaching foundational material that likely was mastered years before but then forgotten.

Spaced Learning

So how can students’ forgetting be reduced? The spacing effect – a promising strategy from the field of cognitive psychology – might hold some of the answers.[4] Research has demonstrated that information is remembered two to three times better if study sessions are spaced in time rather than massed together. For example, learning a unit of classroom material in two 30-minute sessions, where the unit is learned and then reviewed a few days later, will result in greater retention of the material than overlearning the same unit in a single one-hour session. Notably, both scenarios use the same amount of classroom time, and there is no change in the total amount of curriculum content provided to students.

Successfully implementing the spacing technique in a classroom requires an understanding of why it works. While there is no unified spacing theory yet, one account explains this effect in the following way: When our brain encodes information, it associates the information being learned with recently studied material and other contextual cues present in the learning environment (e.g., the instructor’s tone while lecturing, chalk colour, etc.).[5] If the same material is presented twice and those presentations are too close together (crammed), the second presentation is likely to have (a) the same contextual cues associated with it and (b) might not even get the attention it deserves, instead being deemed repetitive and boring.[6] Thus, when two study sessions are crammed together, time spent learning the second presentation might not be used to its full potential.

In a spaced learning approach, however, students learn a set of material on two or more distinct occasions, thereby gaining additional mental routes/memory traces by which to access that information. The more memory traces the brain has leading to particular information, the easier it is to recall that information at a later time. Furthermore, it is desirable to present information in a way that ties current material with students’ prior knowledge – that is, by way of well-established mental routes. Similarly, it is desirable to present concepts in a slightly different manner at each learning occasion to encourage generation of additional mental routes. Presenting material in a different manner and on different occasions will not only strengthen the memory trace, it will also create connections with other pertinent information, thereby deepening the understanding of a concept.

Presenting material in a different manner and on different occasions will not only strengthen the memory trace, it will also create connections with other pertinent information, thereby deepening the understanding of a concept.

For instance, if students are taught a simple fact – light travels at approximately 300 million meters/second – they might find it hard to imagine just how fast that is or to remember this information as a stand-alone fact. But by presenting that information again, in a different manner, in a different context – for example, suggesting that if traveling at the speed of light, one could travel around the Earth seven times in just one second – the fact might become more memorable and also provide an alternative means of retrieving that information when needed. In other words, by connecting the speed of light information to previously learned material on the circumference of the Earth, students have a greater chance of retrieving the speed of light information and developing a deeper understanding of the material in a structure where new and old material are now integrated.

A question that logically follows is: How much time should there be between learning episodes? Again, we can look at why spacing works. Another spacing theory postulates that the initial learning of the material is often superficial, based on simple features of the material that are slippery and difficult to maintain at one’s grasp. When presented with material a second time, the brain attempts to reconstruct the initial learning environment. The longer the delay between first and second learning episode, the more difficult and elaborate is the reconstruction process, and thus the more strongly remembered is the material that is being relearned.[7] The ideal delay between learning episodes is long enough to make relearning difficult, but not so long that the material has been forgotten. Our research suggests that for simple fact learning, delays of a week to a month between learning episodes are about right to reach an almost-forgotten state and thus maximally promote long-term retention;[8] however, this recommendation should be adjusted based on experience with the particular body of students and the difficulty of the material. Complex and difficult material might benefit from a somewhat shorter spacing interval.

Spacing can be incorporated into curriculum in a number of ways, such as introducing cumulative tests and providing delayed homework assignments. For example, in an English class, students could learn the rules of punctuation for commas one week and apostrophes and semicolons in the following weeks. A homework assignment or test that asks students to find mistakes in a passage that incorporates all three types of punctuation will reinforce the later-learned rules, while also spacing out the earlier rules. Each time material is revisited, the student has an opportunity to add a new memory trace, making the material more memorable and more likely to be recalled in the future. Thus, repeated, cumulative tests and homework assignments are better learning tools than a single, discrete midterm or final exam. 

Consistent weekly assignments and/or tests allow for continuous spaced review of already-learned topics. Depending on curriculum constraints, spacing can be introduced within a semester, within a week, or even within a single class. Even introducing a topic at the beginning of a class, and re-introducing it again at the end, will help students forget less. The more often a concept is reviewed, and the more this review is spaced over time, the better chance the concept has of being retained in later grades.

The Testing Effect

The testing effect is another research-based teaching strategy that is often used in conjunction with spacing to minimize students’ forgetting. Studies on the testing effect show that testing students on classroom material is a much more effective strategy than having students re-read or even be re-taught the same information. Actively recalling information from memory is a harder task than simply re-reading or listening to the information again. This forceful retrieval process aids in strengthening the memory trace, leading to deeper, more meaningful encoding. For instance, giving students a short quiz at the end of the class, on the topic learned during the class, will help students remember the information better than simply re-teaching the same topic. 

Actively recalling information from memory is a harder task than simply re-reading or listening to the information again. This forceful retrieval process aids in strengthening the memory trace, leading to deeper, more meaningful encoding.

In terms of specific testing techniques, it has been shown that short-answer tests lead to higher retention than multiple-choice tests.[9] Short-answer tests require students to recall rather than recognize a correct answer. In other words, students are forced to engage in a harder exercise that consequently will lead to strengthening of the memory trace for that particular information. Short-answer testing does not necessarily lead to additional grading; it can be done in an informal manner, through interactive in-class games, such as completing a crossword puzzle as a class at the end of the lesson or playing a trivia-type game. (For an easy way to compile crosswords, try free online puzzle makers).

When short on time, even a brief thought paper at the end of the class answering the question “What are the three most important things you’ve learned during today’s class?” can aid retention, by providing spaced retrieval practice and encouraging formation of connections between the entirety of the material from that day’s class. To reduce teacher workload (these might add up!), thought papers could be marked for completion only and count for a small portion of the grade. We have data that suggests that evaluating tests for completion rather than correctness takes the stress out of the test situation and leads to better experience with the course, at least in university students. 

Feedback Techniques

Feedback completes our trifecta of techniques that reduce forgetting, alongside spacing and testing. Providing feedback after an incorrect response increases students’ performance during the learning session and leads to a significant increase in long-term retention.[10]After all, an incorrect answer left uncorrected will never be properly learned.

But does it matter when students are provided with feedback? The optimal timing varies depending on whether a new concept was successfully learned at the initial learning session (e.g., during a class lecture). A student who masters a concept at initial learning will benefit most from delayed feedback since delayed feedback is a form of spaced re-learning. For instance, if the results of a pop-quiz given at the end of class showed that students understood the material well, it will be better to return those quizzes to students later rather than sooner. When students receive marked quizzes, let’s say a week later, it will force them to return to the previously learned material, thus reaping the benefits of spaced review. In contrast, if students struggle with a concept during initial learning, they will benefit more if feedback is provided immediately. In this way, misunderstanding of the concept is fixed right away, before it has a chance of solidifying and turning into an enduring memory. 

Putting it Together

In an ideal world, with no external constraints or factors acting upon a classroom, where all students come on time and pay attention during class, and where teachers are paid for all the extra hours they put in, a lesson might look something like this:

Mr. Smith is covering a unit on environmental geography. Today, his students will learn the process by which clouds form and the different types of clouds. Mr. Smith first introduces the concept of cloud formation. To keep his students’ attention, he speaks for not more than 15 minutes after which time students complete a short review activity related to cloud formation (e.g., Mr. Smith leads a two-minute Q&A session) to ensure his students have understood the concept. Next, Mr. Smith introduces different types of clouds followed by a short class cloud-categorization task. He completes the lesson of the day by reviewing, with the help of a short answer/fill-in-the blank/crossword quiz covering key concepts. A few items on the quiz are taken from a topic covered during the previous class. He finishes off the class by taking up the quiz. 

We surely do not live in an ideal world, but we do live in a world of technology. Parts of this ideal scenario that cannot be completed in the classroom can be completed as short online homework assignments or self-check quizzes. For example, using an online survey engine for homework assignments that are marked for completion only is an easy way to incorporate spaced review sessions within any classroom. Summary tools of the survey engines also can act as a quick mid-point check for teachers to see which concepts are well-learned and which need more review in the classroom.

Spacing, testing, and feedback are well-studied strategies in cognitive psychology that have received a great deal of empirical support over many decades. In fact, in a recent synthesis of over 800 studies investigating successful influences on student achievement, feedback and spacing ranked fourth and fifth, respectively, out of 49 teaching-related factors.[11] We believe that these strategies can considerably aid recall and help our students achieve greater academic success. We encourage you to provide your students with opportunities for spaced learning in your own classroom – expand mental routes, create new memory traces, and use all the environmental cues you can get your hands on to help your students forget forgetting! 

How do you employ spacing, testing, and feedback techniques in your classroom? Let us know!

For feedback and comments on this article, please e-mail ncepeda@yorku.ca

EN BREF - Comment peut-on aider les élèves à mieux retenir? L’effet d’espacement – une stratégie prometteuse en psychologie cognitive – pourrait receler quelques réponses. Des recherches démontrent que l’information est de deux à trois fois mieux retenue si les séances d’études sont espacées dans le temps plutôt que massées ensemble. L’effet des tests est une autre stratégie d’enseignement fondée sur la recherche et souvent utilisée avec l’espacement pour atténuer les oublis. Il est plus difficile de se rappeler activement de l’information à partir de la mémoire que de la relire ou de la réécouter. Ce vigoureux processus de récupération renforce la trace mnésique, assurant un encodage plus profond et signifiant. Enfin, faire des commentaires opportuns après une mauvaise réponse rehausse le rendement des élèves pendant la séance d’apprentissage, augmentant considérablement la rétention à long terme.


[1] Harold E. Jones, “Experimental Studies of College Teaching,” Archives of Psychology 68, no. 1 (1923): 1-71.

[2] Hermann Ebbinghaus. Memory: A Contribution to Experimental Psychology (New York: Teacher’s College, Columbia University, 1885).

[3] Carl E. Wieman and Katherine Perkins, “Transforming Physics Education,” Physics Today 58, no. 11 (2005): 36-41.

[4] Nicholas J. Cepeda, Harold Pashler, Edward Vul, John T. Wixted, and Doug Rohrer, “Distributed Practice in Verbal Recall Tasks: A Review and Quantitative Synthesis,” Psychological Bulletin 132, no. 3 (2006): 354-380.

[5] Arthur M. Glenberg, “Component-Levels Theory of the Effects of Spacing of Repetitions on Recall and Recognition,” Memory & Cognition 7, no. 2 (1979): 95-112.

[6] Frank N. Dempster, “The Spacing Effect: A Case Study in the Failure to Apply the Results of Psychological Research,” American Psychologist 43, no. 8 (1988): 627-634.

[7] Samuel J. Thios, and Paul R. D’Agostino, “Effects of Repetition as a Function of Study-Phase Retrieval,” Journal of Verbal Learning and Verbal Behavior 15, no. 5 (1976): 529-536.

[8] Nicholas J. Cepeda, Edward Vul, Doug Rohrer, John T. Wixted, and Harold Pashler, “Spacing Effects in Learning: A Temporal Ridgeline of Optimal Retention,” Psychological Science 19, no. 11 (2008): 1095-1102.

[9] Andrew C. Butler, and Henry L. Roediger III, “Testing Improves Long-Term Retention in a Simulated Classroom Setting,” European Journal of Cognitive Psychology 19, no. 4 (2007): 514-527.

[10] Harold Pashler, Nicholas J. Cepeda, John T. Wixted, and Doug Rohrer, “When Does Feedback Facilitate Learning of Words?,” Journal of Experimental Psychology: Learning, Memory, and Cognition 31, no. 1 (2005): 3-8.

[11] John A. C. Hattie. Visible Learning: A Synthesis of Over 800 Meta-Analyses Relating to Achievement (New York: Routledge, 2009).