Desirable Difficulties
Make learning harder now to make knowledge last forever
Desirable difficulties are learning strategies that feel harder and slower in the moment but produce far deeper and more durable understanding. Coined by psychologist Robert Bjork, the concept challenges the widespread assumption that easy, fluent learning is effective learning. In reality, conditions that make performance appear worse during training often make it dramatically better in the long run.
The core desirable difficulties include spacing (distributing practice over time rather than cramming), interleaving (mixing different types of problems rather than practicing one type at a time), generation (attempting to produce answers before being shown them), and testing (retrieving information from memory rather than re-reading). Each of these strategies feels frustrating because short-term performance drops, but they force the brain to build stronger, more flexible mental structures.
A study at the U.S. Air Force Academy found that students who learned from professors who made learning feel easy and who earned higher grades in introductory courses actually performed worse in subsequent advanced courses. The students who struggled more with 'harder' instructors in the intro courses performed significantly better later. The feeling of learning and actual learning are often inversely related.
- The feeling of learning and actual learning are often inversely related
- Struggle during practice builds stronger neural pathways than fluent repetition
- Spacing practice across time beats massing it together, even though massing feels more productive
- Mixing different problem types during practice (interleaving) builds the ability to discriminate and select appropriate strategies
- Attempting to generate answers before being shown them enhances memory even when the attempt fails
- Space your practiceDistribute learning sessions over time rather than cramming. Allow some forgetting to occur between sessions. The effort of re-learning after partial forgetting creates stronger memory traces.Pro tipA 2008 review found that the optimal spacing gap is 10-20% of the time you want to remember something. For a test in one month, space sessions about 3 days apart.WarningSpacing feels less productive because you partially forget between sessions. Trust the research: the struggle of retrieval is the learning.
- Interleave problem typesInstead of practicing one type of problem until mastery before moving to the next (blocking), mix different types together. This forces you to identify which strategy applies to each problem, not just execute a known strategy.Pro tipIn one study, 80% of students rated blocking as more effective than interleaving, even after interleaving produced better test scores. Your feelings about what works are unreliable.
- Generate before you lookBefore reading a chapter, looking at a solution, or receiving instruction, attempt to answer the question or solve the problem yourself. Even wrong attempts enhance subsequent learning through the 'hypercorrection effect': the more confident you were in a wrong answer, the better you remember the correction.Pro tipThis works even with completely novel material. Students who attempted to answer questions about a topic before any instruction learned more from the subsequent instruction.
- Test yourself frequentlyReplace re-reading and highlighting with self-testing. Retrieval practice, even when it feels painful, is one of the most powerful learning strategies known. Use flashcards, practice problems, or simply close the book and try to recall what you read.Pro tipTesting works even when you cannot retrieve the answer. The failed retrieval attempt primes your brain to encode the answer more deeply when you encounter it again.
- Resist the urge to evaluate by immediate performanceJudge your learning by long-term retention and transfer to new problems, not by how smooth practice sessions feel. The most effective learning often feels the most frustrating.WarningTeachers and students consistently rate easier, less effective methods as superior. Be prepared to feel like your new approach is not working, even when it is.
Researchers tracked thousands of Air Force Academy cadets through introductory and advanced calculus courses. Students whose introductory professors made material feel easy earned higher intro grades but performed significantly worse in follow-on courses. Students who struggled more under harder intro professors did better in advanced courses.
Researchers compared students who spaced their Spanish vocabulary practice versus those who massed it. The massed practice group felt more confident and performed better in the short term.
Robert Bjork coined the term after decades of research showing that conditions which slow the apparent rate of learning actually enhance long-term retention and transfer. Epstein illustrates the concept through multiple studies: Air Force Academy cadets who struggled more in introductory courses performed better in advanced ones; Spanish vocabulary learners who spaced their practice remembered more eight years later; math students who interleaved problem types performed worse during practice but dramatically better on tests. The key finding that runs through all the research is what Bjork calls the distinction between learning (durable, flexible knowledge) and performance (momentary, context-dependent ability).