Demystifying desirable difficulties 1: What they are

Mirjam Neelen & Paul A. Kirschner

Desirable difficulties, a term coined by Robert Bjork in 1994, has gained traction. This is great because desirable difficulties have been shown to be important for learning and learning design. As Bjork explains in this video, they’re desirable because they enhance the very target of training and instruction, namely long-term retention and transfer of knowledge and skills. And they’re difficulties because they pose challenges for the learner.

Unfortunately, desirable difficulties are also often misunderstood or have been diluted to whatever people consider to be ‘desirable difficulties’ in plain language. This also happened to Anders Ericsson’s concept of deliberate practice[1] where people think that if you practice ‘on purpose’ (and not accidentally?) that the practice was deliberate and that it was, thus, deliberate practice. In the context of desirable difficulties, we’ve seen many examples where people moved away from how Bjork defined and intended it, and just use the term as ‘layman’s language’. To us, it doesn’t make sense to take a theory and then run with it, making it into something else. Doing this often leads to improper use, a loss of efficacy and power, and even lethal mutations[2].

Understanding a theory for what it is and isn’t helps us to have clear discussions and make well-informed design decisions. In short, as Donald Clark (2022) says so eloquently in his book ‘Learning Experience Design’: “Ignorance or avoidance of theory within learning design practice begs the question – what practice?” (p. 4)

In this 2-part blog, we attempt to clear the fog, demystifying what Robert Bjork, and later with his wife and co-researcher Elizabeth Bjork actually meant when they wrote about and studied desirable difficulties (as have many others!), hoping that we can stick to their definition and call the ‘other things’… other things.

Today, blog 1 (Demystifying desirable difficulties 1: What they are) and shortly, blog 2 (Demystifying desirable difficulties 2: What they’re NOT).

What desirable difficulties are

Here’s a sentence to muse on (phrased by the Bjork’s (2011) themselves:

Conditions of learning that make performance improve rapidly often fail to support long-term retention and transfer, whereas conditions that create challenges and slow the rate of apparent learning often optimize long-term retention and transfer (p. 57).

This critical distinction between performance and learning lies at the root of the idea of desirable difficulties.

Learning is a change in our long-term memory (Kirschner et al., 2006). Learning is lasting and stable, and when ‘forgotten’, it’s still somewhere in your long-term memory so that relearning is facilitated. Performance (or, achievement), on the other hand, is short-term. It’s fragile and often quickly forgotten (like right after an inspiring event, test, or exam) and takes effort to ‘relearn’ (or actually, learn) after it’s been forgotten. There’s been a lot of research done, nicely reviewed and summarised by Soderstrom and Bjork (2015), showing that considerable learning can occur across a period of time while no performance improvement can be observed[3]. The opposite is also true. Both human and non-human animals can show substantial improvements in performance across practice and training sessions, while in the end it turns out they haven’t really learned (which could be revealed, for example, when a learner is invited to perform the task again after a period of time after they completed the training (after a delay) or when they have to perform the task in a different context than the one in which they practiced in the training situation.

Based on the research showing that people can learn while not (yet) demonstrating improved performance and can perform without having learned anything, Bjork and Bjork (2011) came up with the assumption that an item in memory can be characterised by two strengths – storage strength (how embedded or interconnected a memory representation is with related knowledge and skills) and retrieval strength (how easily a memory representation can be activated or accessed when needed). The assumption is that “current performance is entirely a function of current retrieval strength, but that storage strength acts to retard the loss (forgetting) and enhance the gain (relearning) of retrieval strength” (p. 58).

The key idea is that the conditions that most rapidly increase retrieval strength differ from the conditions that maximise the gain of storage strength. If learners interpret current retrieval strength (performance) as storage strength (learning), then they’re fooling themselves. They become prone to preferring poorer conditions of learning (e.g., study strategies such as cramming for a test) to better conditions of learning (e.g., testing yourself intermittently) because they experience ‘success’ (they perform well) using the poorer conditions while they feel that they struggle under the better ones (when they’re actually learning).

The Bjorks went on a mission to figure out what these ‘better conditions’ are; conditions that seem to initially create difficulty but lead to more durable (i.e., improved ‘storage strength’; remembering long-term) and flexible learning (i.e., improved ‘retrieval strength’; being able to apply something at a later moment and/or in different contexts).

These conditions are… desirable difficulties! Bjork and Bjork describe five.

  • Interleaving/Variable practice: Bjork (1994) describes it as ‘varying the conditions of practice’ and explains them as variation and unpredictability in the learning environment. This is about varying the practice of various parameters of a to-be-learned task (Hall and Magill (1995) refer to it as ‘schema enhancement’).

An example. Let’s say a learner needs to practice using Booleans to do a literature search or logic class, perhaps how to use Boolean operators. The first operator is ‘AND’ so let’s call this task A. So-called ‘blocked practice’ (repeating using the AND-operator over and over again) will lead to quicker performance. However, when learners practice other, related things in between (for example, perhaps they also need to learn how to use the ‘OR’ operator of the ‘NOT’ operator in a search – let’s call this tasks B and C), it will take them seemingly longer to learn task A, and B, and C individually but in the end, they will learn it better and therefore, in the end their performance will be better in the long run as the need to use all of the operators in their work or study.  

  • Contextual interference: The contextual interference effect (doing the same thing often but in different situations or contexts) was first demonstrated by Battig (1966). It’s very similar to interleaving but here you make the task environment – not the task itself – more variable or unpredictable in a way that creates a temporarily interference for the learner (Kirschner et al., 2022). By the way, did you know that even studying the same material in two different rooms leads to increase recall of that material? Pretty amazing.
  • Spaced practice: This is also knowns as ‘distributed practice’ and is about spacing learning over time. Distributing practice (e.g., learning tasks, study attempts, training trials) supports long-term retention. We wrote a blog on spaced practice back in 2017, in case you’d like to read a bit more.
  • Reduced feedback: This refers to the finding that reducing the frequency of feedback makes life more difficult for learners during training but – as with all desirable difficulties – can enhance long-term performance. It stimulates their independence, knowing that the instructor won’t give them the answer in the end. Examples of ‘reducing’ feedback are giving summary feedback at the end of a practice session or ‘fading’ the frequency of feedback over sessions.
  • Retrieval practice/Practice testing: In a nutshell, practice testing ‘forces’ learners to try to recall what they’ve previously learned from memory. Because they actively remember that information – retrieve it from their memory – they can remember it better and longer. We recently published a blog on the very topic.

This is what desirable difficulties are. They’re about conditions that create certain types of challenges, focused on slowing the rate of apparent learning so that long-term retention and transfer are optimised (Bjork & Bjork, 2020). They call it ‘making it difficult but in a good way’. Sporters might call it ‘No pain, No gain’.

In our next blog, we’ll discuss where things get confused; where people talk about ‘desirable difficulties’, while they actually mean something else.


Battig, W. F. (1966). Facilitation and interference. In E.A. Bilodeau (Ed.), Acquisition of skill (pp.215-244). Academic Press.

Bjork, R.A. (1994). Memory and metamemory considerations in the training of human beings. In J. Metcalfe and A. Shimamura (Eds.), Metacognition: Knowing about knowing (pp. 185-205). MIT Press.

Bjork, R. A., & Bjork, E. L. (2020). Desirable difficulties in theory and practice. Journal of Applied Research in Memory and Cognition, 9(4), 475-479.

Bjork, E. L., & Bjork, R. A. (2011). Making things hard on yourself, but in a good way: Creating desirable difficulties to enhance learning. Psychology and the real world: Essays illustrating fundamental contributions to society, 2, 59-68.

Clark, D. (2022). Learning experience design: How to create effective learning that works. Kogan Page Publishers.

Ericsson, K. A., Krampe, R. T., & Tesch-Römer, C. (1993). The role of deliberate practice in the acquisition of expert performance. Psychological Review, 100(3), 363–406.

Hall, K. G., & Magill, R. A. (1995). Variability of practice and contextual interference in motor skill learning. Journal of motor behavior, 27(4), 299-309.

Kirschner, P. A., Hendrick, C., & Heal, J. (2022). How teaching happens: Seminal works in teaching and teacher effectiveness and what they mean in practice. Routledge. Soderstrom, N. C., & Bjork, R. A. (2015). Learning versus performance: An integrative review. Perspectives on Psychological Science, 10(2), 176-199.

[1] Anders Ericsson et al. (1993) define deliberate practice as “a highly structured activity, the explicit goal of which is to improve performance. Specific tasks are invented to overcome weaknesses, and performance is carefully monitored to provide cues for ways to improve it further…[it] requires effort and is not inherently enjoyable. Individuals are motivated to practice because practice improves performance.” (p/ 368)

[2] The modification of ideas and techniques to such an extent that they’re so far removed from the original concept or suggestion that it is no longer effective, or even counterproductive.

[3] Here’s a problem, namely that performance is often easy to see and measure (a score on a test) while real learning isn’t.


5 thoughts on “Demystifying desirable difficulties 1: What they are

  1. Dr. Jim Sellner PhD., DipCoaching says:

    Excellent insightful useful difficult to absorb desirably LOL

    Thank you 




    div dir=”ltr”>Dr. Jim Sellner, PhD.,DipC. EVP, Peop


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