The Spacing Effect: How to Improve Learning and Maximize Retention
Reading Time: 12 minutes
We are not taught how to learn in school, we are taught how to
pass tests. The spacing effect is a far more effective way to learn and
retain information that works with our brain instead of against it. Find
out how to use it here.
“Every perception is to some degree an act of creation, and every act of memory is to some degree an act of imagination.”
— Gerald Edelman, Second Nature: Brain Science and Human Knowledge
The most important metaskill you can learn is how to learn. Learning
allows you to adapt. As Darwin hinted, it’s not the strongest who
survives. It’s the one who easily adapts to a changing environment.
Learning how to learn is a part of a “work smarter, not harder” approach
to life—one that probabilistically helps you avoid becoming irrelevant.
Your time is precious, and you don’t want to waste it on something
which will just be forgotten.
During the school years, most of us got used to spending hours at a
time memorizing facts, equations, the names of the elements, French
verbs, dates of key historical events. We found ourselves frantically
cramming the night before a test. We probably read through our notes
over and over, a gallon of coffee in hand, in the hope that the
information would somehow lodge in our brains. Once the test was over,
we doubtless forgot everything straight away.1
Even outside of formal education, we have to learn large amounts of
new information on a regular basis: foreign languages, technical terms,
sale scripts, speeches, the names of coworkers. Learning through rote
memorization is tedious and—more important—ineffective. If we want to
remember something, we need to work with our brains, not against them.
To do that, we need to understand cognitive constraints and find
intelligent ways to get around them or use them to our advantage.
This is where the spacing effect comes in. It’s a wildly useful
phenomenon: we are better able to recall information and concepts if we
learn them in multiple, spread-out sessions. We can leverage this effect
by using spaced repetition to slowly learn almost anything.
It works for words, numbers, images, and skills. It works for anyone
of any age, from babies to elderly people. It works for animals, even
species as simple as sea slugs. The effect cuts across disciplines and
can be used to learn anything from artistic styles to mathematical
Spaced repetition might not have the immediacy of cramming or the
adrenaline rush of a manic all-nighter. But the information we learn
from it can last a lifetime and tends to be effectively retained. In
some ways, the spacing effect is a cognitive limitation, yet a useful
one—if we are aware of it.
In Fluent Forever: How to Learn Any Language and Never Forget It, Gabriel Wyner writes:
Spaced repetition…[is] extraordinarily efficient. In a
four-month period, practising for 30 minutes a day, you can expect to
learn and retain 3600 flashcards with 90 to 95 percent accuracy. These
flashcards can teach you an alphabet, vocabulary, grammar, and even
pronunciation. And they can do it without becoming tedious because
they’re always challenging enough to remain interesting and fun.
In Mindhacker, Ron and Marty Hale-Evans explore further:
Our memory is simultaneously magnificent and pathetic. It
is capable of incredible feats, yet it never works quite like we wish
it would. Ideally, we would be able to remember everything instantly,
but we are not computers. We hack our memory with tools like memory
palaces, but such techniques required effort and dedication. Most of us
give up, and outsource our memory to smartphones, cloud enabled
computers, or plain old pen and paper. There is a compromise…a learning
technique called spaced repetition which efficiently organizes
information or memorization and retention can be used to achieve near
“If you wish to forget anything on the spot, make a note that this thing is to be remembered.”
— Edgar Allan Poe, Marginalia
The Discovery of The Spacing Effect
Hermann Ebbinghaus (1850-1909),
a German psychologist and pioneer of quantitative memory research,
first identified the spacing effect. After earning his PhD in Germany,
he traveled to London. Like so many people, he found his life forever
changed by a book.
The work in question was Elements of Psychophysics
by the pioneering experimental psychologist Gustav Fechner. Inspired by
this book, Ebbinghaus began the research into memory that would consume
his career and impact all of us.
Ebbinghaus took up his new field of study with the unbridled zest of a
newcomer. He didn’t believe strongly in the prevailing understanding of
memory at the time. In his wish to avoid getting bogged down in theory,
he made everything about experimentation. As researcher and the sole
subject of his experiments, he faced an uphill battle.
His most important findings were in the areas of forgetting and
learning curves. These are graphical representations of the process of
learning and forgetting. The forgetting curve shows how a memory of new
information decays in the brain,2 with the fastest drop occurring after 20 minutes and the curve leveling off after a day.
There is a way to slow down the process of forgetting. We need only
to recall or revisit the information after we originally come across it.
Going over the information later, at intervals, helps us remember a
greater percentage of the material. Persistence will allow us to recall
with 100% accuracy all that we want to remember.
The learning curve is the inverse. It illustrates the rate at which we learn new information.
When we use spaced repetition, the forgetting curve changes:
Frequency matters. Under normal conditions, frequent
repetitions aid memory. We know this intuitively. Just try to memorize
this article on a single repetition. However much attention, focus, or
individual ability you have, it won’t work.
Memory mastery comes from repeated exposure to the material.
Ebbinghaus observes, “Left to itself every mental content gradually
loses its capacity for being revived, or at least suffers loss in this
regard under the influence of time.” Cramming is not an effective
memorization strategy. Lacking the robustness developed in later
sessions, crammed facts soon vanish. Even something as important and
frequently used as language can decay if not put into use.
There are other ways to improve memory. Intensity of emotion matters,
as does the intensity of attention. Ebbinghaus notes in his definitive
work on the subject, Memory and Forgetting:
Very great is the dependence of retention and reproduction upon the intensity of the attention and interest which were attached to the mental states the first time they were present.
The burnt child shuns the fire, and the dog which has been beaten runs
from the whip, after a single vivid experience. People in whom we are
interested we may see daily and yet not be able to recall the colour of
their hair or of their eyes…Our information comes almost exclusively from the observation of extreme and especially striking cases.
Ebbinghaus also uncovered something extraordinary: even when we
appear to have forgotten information, a certain quantity is stored in
our subconscious minds. He referred to these memories as savings. While
they cannot be consciously retrieved, they speed up the process of
relearning the same information later on.
A poem is learned by heart and then not again repeated.
We will suppose that after a half year it has been forgotten: no effort
of recollection is able to call it back again into consciousness. At
best only isolated fragments return. Suppose that the poem is again
learned by heart. It then becomes evident that, although to all
appearances totally forgotten, it still in a certain sense exists and in
a way to be effective. The second learning requires noticeably less
time or a noticeably smaller number of repetitions than the first. It
also requires less time or repetitions than would now be necessary to
learn a similar poem of the same length.
As the first researcher to undertake serious experimentation on
memory and why we forget, Ebbinghaus transformed psychology as a new
branch of science. His impact has been compared to that of Aristotle.
Ongoing research into the spacing effect continues to support
“There is no such thing
as memorizing. We can think, we can repeat, we can recall and we can
imagine, but we aren’t built to memorize. Rather our brains are designed
to think and automatically hold onto what’s important. While running
away from our friendly neighborhood tiger, we don’t think “You need to
remember this! Tigers are bad! Don’t forget! They’re bad!” We simply run
away, and our brain remembers for us.”
— Gabriel Wyner, Fluent Forever: How to Learn Any Language and Never Forget It
How the Spacing Effect Works
Let’s take a quick refresher on what we know about how memory in works, because it’s not what we think.
Memories are not located in any one part of the brain. Memories are
formed in a process which involves the entire brain. If you think about
your favorite book, different parts of your brain will have encoded the
look of it, the storyline, the emotions it made you feel, the smell of
the pages, and so on. Memories are constructed from disparate components
which create a logical whole. As you think about that book, a web of
neural patterns pieces together a previously encoded image. Our brains
are not like computers – we can’t just ‘tell’ ourselves to remember
In Mastery, Robert Greene explains:
In the end, an entire network of neurons is developed to
remember this single task, which accounts for the fact we can still ride
a bicycle years after we first learned how to do so. If we were to take
a look at the frontal cortex of those who have mastered something
through repetition, it would be remarkable still and inactive as they
performed the skill. All their brain activity is occurring in areas that
are lower down and required much less conscious control…People who do
not practice and learn new skills can never gain a proper sense of
proportion or self-criticism. They think they can achieve anything
without effort and have little contact with reality. Trying something
over and over again grounds you in reality, making you deeply aware of
your inadequacies and of what you can accomplish with more work and
No definitive answer has been found to explain how the spacing effect works. However, a number of factors are believed to help:
Forgetting and learning are, in a counterintuitive twist, linked.
When we review close to the point of nearly forgetting, our brains
reinforce the memory as well as add new details. This is one reason
practice papers and teaching other people are the most effective ways
for students to revise—they highlight what has been forgotten.
Retrieving memories changes the way they are later encoded.
In essence, the harder something is to remember now, the better we will
recall it in the future. The more we strain, which is painful mental
labor, the easier it will be in the future. There is no learning without
pain. Recall is more important than recognition. This explains why
practice tests are a better way to learn than opening your text and
re-reading your highlights.
Our brains assign greater importance to repeated information.
This makes sense; information we encounter on a regular basis does tend
to be more important than that which we only come across once.
Disregarding any forms of mental impairment, we don’t have trouble
recalling the information we need on a daily basis. Our PIN, our own
telephone number, the directions to work, and names of coworkers, for
example. We might once have struggled to remember them, but after
accessing those sorts of information hundreds or thousands of time,
recall becomes effortless.
Some researchers also believe that semantic priming is a factor.
This refers to the associations we form between words which make them
easier to recall. So, the sentence ‘the doctor and the nurse walked
through the hospital’ is easier to remember than ‘the doctor and the
artist walked through the supermarket’ because the words ‘doctor’
‘nurse’ and ‘hospital’ are linked. If you are asked to remember a
logical sentence such as ‘mitochondria is the powerhouse of the cell’,
it’s not too difficult. If those same words are scrambled and become
‘cell the house mitochondria power is of’ it’s a lot harder to remember.
And if those words are broken up into nonsensical syllables – ‘th ell
ce he ous hon mit odria fi of’ – retaining them would become arduous.
But some researchers have theorised that repetition over time primes us
to connect information. So, if you revised ‘th ell ce he ous hon mit
odria fi of’ enough times, you would start to connect ‘th’ and ‘ell.’ We
can demonstrate semantic priming by telling a friend to say ‘silk’ ten
times, then asking them what a cow drinks. They will almost certainly
say ‘milk.’ The answer is, of course, water.
Yet another theory is that of deficient processing.
Some literature points to the possibility that spaced repetition is not
in itself especially efficient, but that massed learning is just very
inefficient. By comparison, spaced repetition seems special when it is,
in fact, a reflection of our true capabilities. Researchers posit that
massed learning is redundant because we lose interest as we study
information and retain less and less over time. Closely spaced
repetition sessions leverage our initial interest before our focus
With properly spaced repetition, you increase the intervals of time
between learning attempts. Each learning attempt reinforces the neural
connections. For example, we learn a list better if we repeatedly study
it over a period of time than if we tackle it in one single burst. We’re
actually more efficient this way. Spaced sessions allow us to invest
less total time to memorize than one single session, whereas we might
get bored while going over the same material again and again in a single
session. Of course, when we’re bored we pay less and less attention.3
In Focused Determination, the authors explain why variety also contributes to deficient processing.
There is also minimal variation in the way the material
is presented to the brain when it is repeatedly visited over a short
time. This tends to decrease our learning. In contrast, when repetition
learning takes place over a longer period, it is more likely that the
materials are presented differently. We have to retrieve the previously
learned information from memory and hence reinforce it. All of this
leads us to become more interested in the content and therefore more
receptive to learning it.
“How do you remember
better? Repeated exposure to information in specifically timed intervals
provides the most powerful way to fix memory into the brain.
…Deliberately re-expose yourself to the information more elaborately,
and in fixed, spaced intervals, if you want the retrieval to be the most
vivid it can be. Learning occurs best when new information is
incorporated gradually into the memory store rather than when it is
jammed in all at once.”
— John Medina, Brain Rules
Taking Advantage of the Spacing Effect
We don’t learn about spaced repetition in school—something which
baffles many researchers. Most classes teach a single topic per session,
then don’t repeat it until the test.
Going over a topic once teaches very little—sometimes nothing at all,
if the teacher is unengaging or the class is too long. Most teachers
expect their students to take care of the memorizing part themselves. As
a result, many of us develop bad learning habits like cramming to cope
with the demands of our classes.
We need to break up with cramming and focus on what actually works: spaced repetition.
The difficulty of spaced repetition is not effort but that it
requires forward planning and a small investment of time to set up a
system. But in the long run, it saves us time as we retain information
and spend less total time learning.
A typical spaced repetition system includes these key components:
- A schedule for review of information. Typical
systems involve going over information after an hour, then a day, then
every other day, then weekly, then fortnightly, then monthly, then every
six months, then yearly. Guess correctly and the information moves to
the next level and is reviewed less often. Guess incorrectly and it
moves down a level and is reviewed more often.
- A means of storing and organizing information.
Flashcards or spaced repetition software (such as Anki and SuperMemo)
are the most common options. Software has the obvious advantage of
requiring little effort to maintain, and of having an inbuilt repetition
schedule. Anecdotal evidence suggests that writing information out on
flashcards contributes to the learning process.
- A metric for tracking progress. Spaced repetition
systems work best if they include built-in positive reinforcement. This
is why learning programs like Duolingo and Memrise incorporate a points
system, daily goals, leaderboards and so on. Tracking progress gives us a
sense of progression and improvement.
- A set duration for review sessions. If we practice
for too long, our attention wanes and we retain decreasing amounts of
information. Likewise, a session needs to be long enough to ensure
focused immersion. A typical recommendation is no more than 30 minutes,
with a break before any other review sessions.
The spacing effect is a perfect example of how much more effective we
can be if we understand how our minds work, and use them in an optimal
way. All you need to learn something for life are flashcards and a
schedule. Then, of course, you’re free to move on to actually applying
and using what you’ve learned.
Tagged: Gabriel Wyner, Gustav Fechner, Hermann Ebbinghaus, Memory, Robert Greene
- 1 When is the last time you used a2+ b2= c2 in real life?
- 2 This is different than
the half-life of knowledge, the process by which information in memory
becomes less valuable because your understanding of the world has
- 3 You can test this by asking yourself what your last meeting yesterday was about.