WordieWhat Are Desirable Difficulties?
Desirable Difficulties: learning conditions that slow down or complicate practice in the short term, such as spacing, testing or interleaving, but lead to better long-term retention and transfer.
Also known as: desirable difficulty, productive difficulty
Desirable difficulties are ways of studying that make practice feel harder and slower but produce better learning in the long run. Spacing your reviews, testing yourself and mixing topics all reduce how well you seem to do today while increasing what you still know in a month. The term was coined by psychologist Robert Bjork in 1994.
Where the idea comes from
Bjork noticed a gap between performance (how well you do during practice) and learning (the lasting change you can show later). Conditions that make practice smooth often produce weak learning, and conditions that make it rough often produce strong learning. Teachers and learners tend to choose the smooth ones, because they look like progress.
Robert and Elizabeth Bjork's "new theory of disuse" (1992) gives a framework. Every memory has two strengths:
- Storage strength: how well-established and connected the memory is. It only grows.
- Retrieval strength: how easily you can access it right now. It rises and falls.
The key claim is that retrieving a memory when retrieval strength is low adds more storage strength than retrieving it when it is high. Reviewing a word you just saw is easy and adds little; recalling one you have half-forgotten is hard and adds a lot.
Common desirable difficulties
| Difficulty | Easy alternative | For vocabulary |
|---|---|---|
| Spacing | Massed practice (cramming) | Review words over days, not in one sitting |
| Retrieval practice | Rereading | Recall the meaning before you look |
| Interleaving | Blocked practice | Mix similar words in one review set |
| Generation | Being given the answer | Guess a word's meaning from context first, then check |
| Varied practice | Same format every time | Switch between flashcards, cloze sentences and writing |
A vocabulary example
You are learning affect, effect, infer and imply.
- Easy version: study each word's card five times in a row, then move on. By the end you get every card right.
- Desirable-difficulty version: shuffle all four into one deck, try to recall each meaning before flipping, write one sentence per word from memory, and repeat the quiz three days later.
The second version produces more errors on day one, especially between infer and imply. That confusion forces you to notice the difference ("the speaker implies, the listener infers"), which is exactly what you need when reading or writing.
Why it matters for learning words
Vocabulary study is full of comfortable habits that feel productive: rereading word lists, copying definitions, reviewing cards you already know. Bjork's work explains why those habits disappoint. It also helps you interpret your own experience. If a review session feels effortful and you miss some words, that is not a sign the method is failing. It is often a sign the gaps are about right.
When difficulty is not desirable
The word "desirable" matters. A difficulty helps only if you can still succeed, at least with effort, and if it engages the processes you want to strengthen. Examples of undesirable difficulty:
- Reading texts where you know too few words to follow the meaning, so nothing can be inferred.
- Gaps so long that every word has to be relearned from zero.
- Tests with no feedback on material you never learned.
- Unrelated noise, like studying in a distracting environment.
How to apply it
- Expect some failure in every review session; aim for most recalls to succeed after real effort.
- Prefer recall to recognition and recognition to rereading.
- Space reviews with an expanding schedule; the spaced repetition scheduler can help.
- Judge methods by a delayed test, not by how the session felt.
The spacing effect research article covers the evidence behind the most important difficulty in detail.
Sources: Bjork, R. A. (1994). Memory and metamemory considerations in the training of human beings. In Metacognition: Knowing about knowing. Bjork, R. A., & Bjork, E. L. (1992). A new theory of disuse and an old theory of stimulus fluctuation.
Frequently asked questions
Who coined the term desirable difficulties?
Robert A. Bjork of UCLA introduced the term in 1994. Much of the related theory was developed with Elizabeth Ligon Bjork.
What are examples of desirable difficulties?
Spacing study sessions, testing yourself instead of rereading, interleaving different topics, generating answers before seeing them, and varying the conditions of practice.
When is a difficulty undesirable?
When the learner cannot respond successfully at all. Material far beyond your level, or a word list with no meaning or context, makes learning harder without making it stronger.
Why do desirable difficulties feel like they are not working?
Because they lower performance during practice. Learners judge progress by how fluent practice feels, so the methods that build durable memory often feel less effective than easy rereading.
Related terms
Spacing Effect
the finding that information studied in several sessions spread out over time is remembered far better than the same amount of study packed into one session.
Interleaving
a practice schedule that mixes different topics, skills or problem types within a session (ABCABC) instead of finishing one before starting the next (AAABBBCCC).
Retrieval Practice
a learning strategy in which you practice bringing information back to mind, through quizzes, flashcards or free recall, because the act of retrieving strengthens memory more than restudying does.
Testing Effect
the research finding that taking a test on material, even with no grade or feedback, improves long-term retention more than spending the same time restudying it.
Massed Practice
studying or practicing the same material in one concentrated block with little or no gap between repetitions, as in cramming the night before a test; the opposite of spaced or distributed practice.
Articles about Desirable Difficulties
The Testing Effect Explained: Why Trying to Remember Beats Studying Again
The testing effect: retrieving information strengthens memory more than restudying it. Key studies, why it works, and how to use it to learn vocabulary.
The Spacing Effect: What 140 Years of Research Says About When to Review
Spacing effect research from Ebbinghaus to Cepeda et al. (2008): what the key studies found about review gaps, and simple rules for spacing vocabulary practice.
The Complete Spaced Repetition Guide for Vocabulary: From First Card to Advanced Settings
A complete spaced repetition guide for vocabulary: intervals that work, daily review load math, Anki and FSRS settings, and how to combine SRS with reading.
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