When you reread your textbook several times the night before an exam, the material flows smoothly, and you feel as if you know it all. Yet when you actually get the exam paper a few days later, the material that felt so familiar doesn't come to mind easily. What we learn easily often fades just as easily, while what we learn with effort tends to stay with us longer.
In education and the learning sciences, a difficulty like this, which makes learning harder in the moment but helps long-term memory and application, is called a desirable difficulty. Put simply, it is the idea that ‘when you deliberately make studying a little harder, you learn more lastingly and more deeply.’
This article explains, in easy-to-understand terms, what desirable difficulty means and where it came from, the main learning methods, why we find the principle hard to believe, and how to apply it in the classroom and everyday life.
How Desirable Difficulty Works, with Examples
Desirable Difficulty According to Robert Bjork
The concept was first named in 1994 by Robert A. Bjork, a cognitive psychologist at the University of California, Los Angeles (UCLA). In a paper on how people are trained, Bjork pointed out that performance during learning and learning that actually lasts can be two different things.
Bjork distinguished between the two with the terms ‘performance’ and ‘learning.’ Performance is the visible results during practice, while learning is the ability that remains after time has passed and can be transferred to new situations. In other words, seeming to do well during practice does not necessarily mean you have truly learned.
According to Bjork, the harder a memory is to retrieve, the stronger it becomes when you overcome that difficulty and retrieve it. So adding the right amount of difficulty to the learning process slows you down for now but creates memories that last.
Learning Methods That Create Desirable Difficulty
Bjork and his colleagues introduced a number of methods that look inefficient on the surface but are highly effective in the long run.
- Spacing: Instead of cramming all at once, you study several times with intervals in between.
- Interleaving: Instead of solving one type of problem after another, you practice with several types mixed together.
- Retrieval practice: Instead of rereading, you close the book and recall the material yourself or try solving problems.
- Generation effect: Instead of looking at the answer right away, you first try to come up with an answer yourself and then check it.
What these methods have in common is that they make you think harder while studying. Spacing means you have to recall material you have partly forgotten in the meantime, and mixing problems means you have to choose for yourself which method to use each time. It is precisely this effort that consolidates memory.
The effect of retrieval practice has been confirmed in many experiments. In a 2006 study by Henry L. Roediger III and Jeffrey D. Karpicke, students who took a test in which they recalled and wrote down what they had read remembered far more a week later than students who simply reread the text. This is why tests are regarded not only as tools for measuring ability but as powerful study methods in their own right.
Why Easy Studying Seems Better
The biggest reason desirable difficulties are not widely used is that learners find it hard to sense their effect for themselves. When we reread the same material, the text grows more and more familiar, and we mistake that familiarity for a sign of understanding. This is commonly called the fluency illusion.
An experiment published in 2008 by Nate Kornell and Robert Bjork illustrates this illusion well. Participants learned the styles of several painters by looking at their paintings, and those who saw the paintings of different artists mixed together were better at identifying the artists of paintings they had never seen than those who saw each artist's paintings in a block.
The interesting part comes next. Even though the test results came out in favor of mixing, many participants still answered that viewing the paintings in blocks had been more effective. In effect, how comfortable studying felt and its actual learning effect moved in opposite directions.
Teachers fall prey to this illusion too. When students solve problems smoothly in class, it is easy to feel that you have taught well, but that may be only momentary performance. Conversely, a lesson in which students struggle and find answers slowly can make a bigger difference a few weeks later.
How to Apply It in the Classroom and Everyday Life
Not every difficulty is desirable, however. Robert and Elizabeth Bjork stress that the word ‘desirable’ matters. If learners lack the basic knowledge to overcome a difficulty, it does not help them learn and leaves only frustration, becoming an ‘undesirable difficulty.’
That is why, in education, the key is adjusting the level of difficulty to the learner's level. Typical approaches include having students recall the previous lesson through a short quiz at the start of class, or having them review by mixing in old problems even after a unit is over. Such quizzes are better used as practice in retrieving memories than as a way of giving grades.
The same applies to studying on your own. Rather than underlining and rereading, close the book and try to say the key points; rather than memorizing everything in one day, review over several days; and rather than repeating similar problems, try solving a mix of different types.
At first, your scores may drop and your progress may slow, which can be unsettling. But that discomfort is less a sign of failure than a sign that memories are taking hold. To check the results, it is a good idea to test yourself a few days later and see how much has actually stuck.
Desirable difficulty tells us that just because studying feels hard does not mean we are doing it wrong. On the contrary, when it feels easy, it is worth doubting it one more time.
Not avoiding the moments when learning feels like a struggle: that is the first step toward learning that lasts.
