Desirable Difficulty
Why struggle is a sign that learning is happening — and how to find the right level of challenge.
Here's something that sounds wrong but is backed by decades of research:
If revision feels easy, you're probably not learning much.
The techniques that feel hardest — testing yourself, spacing out your practice, mixing topics — are exactly the ones that work best. This isn't a coincidence. The difficulty is the point.
What Is Desirable Difficulty?
Desirable difficulty is a term coined by psychologists Robert and Elizabeth Bjork. It describes challenges that make learning harder in the short term but stronger in the long term.
The key word is desirable. Not all difficulty helps learning:
- Trying to learn from a confusing, badly-written textbook? That's just frustrating.
- Studying in a noisy room where you can't concentrate? That's a barrier, not a benefit.
But some types of difficulty genuinely improve learning:
- Having to retrieve information from memory (instead of just reading it)
- Spacing your practice out (instead of cramming)
- Mixing different topics together (instead of blocking)
- Attempting problems before being shown the solution
These feel harder. You make more mistakes. You feel less confident during practice. But when the exam comes, you perform better.
The Effort-Learning Connection
Think about physical exercise. Which builds more muscle:
- Lifting a weight that feels easy?
- Lifting a weight that challenges you?
The challenge is what creates growth. Your muscles don't get stronger from easy movements — they get stronger from being pushed.
Your brain works the same way. Mental effort isn't a sign that something's going wrong; it's a sign that learning is happening.
When you struggle to remember something, your brain strengthens the pathways to that information. When you easily recognise something, those pathways don't change much.
Easy revision = weak learning
Effortful revision = strong learning
Why Easy Feels Better (But Isn't)
Here's the cruel trick: easy revision feels more effective.
| Easy Revision | Hard Revision |
|---|---|
| Re-reading notes | Testing yourself with notes closed |
| High accuracy during practice | More mistakes during practice |
| Feels fluent and smooth | Feels halting and effortful |
| "I know this!" | "I'm not sure..." |
| Fast progress through material | Slow, careful progress |
Students who use easy methods report feeling more confident about their learning. But when tested later, they perform worse than students who struggled during practice.
This is called the illusion of learning: fluency during study makes you think you know something, when really you're just recognising it in a familiar context.
The students who struggled — who made mistakes, who had to think hard, who felt uncertain — actually learned more.
The Desirable Difficulties
Here are the main desirable difficulties that improve learning:
1. Retrieval Practice
Testing yourself instead of re-reading.
Why it's hard: You might not remember. You might get things wrong. It feels uncomfortable.
Why it works: The effort of pulling information from memory strengthens that memory far more than passively reviewing it.
See Retrieval Practice for techniques.
2. Spaced Practice
Spreading revision out over time instead of cramming.
Why it's hard: When you return to something after a gap, you've forgotten some of it. You have to work to remember.
Why it works: That slight forgetting means your brain has to work harder to recall — and that effort deepens the memory.
See Spaced Repetition for how to schedule this.
3. Interleaved Practice
Mixing different topics instead of doing one at a time.
Why it's hard: You can't get into a rhythm. Each problem requires you to identify what type it is. You make more errors.
Why it works: You're practicing the skill of recognising problem types, not just executing known methods. This is exactly what exams require.
See Interleaving for how to mix effectively.
4. Generation (Attempting Before Learning)
Trying to solve a problem before being shown how.
Why it's hard: You might have no idea what to do. You'll probably get it wrong. It feels like wasted effort.
Why it works: Even unsuccessful attempts prime your brain to learn from the solution. You understand why the method works because you've experienced the problem it solves.
5. Variation
Practicing in different contexts, with different problem formats, at different times.
Why it's hard: You can't just repeat the same thing. Each variation requires adaptation.
Why it works: It builds flexible knowledge that transfers to new situations — like the unfamiliar questions in exams.
Applying This to Maths Revision
Before Looking at a Worked Example
Don't just read worked examples. Before looking at the solution:
- Read the question
- Try to solve it yourself (even if you're not sure)
- Get as far as you can
- Then look at the solution
- Compare your attempt to the correct method
Even if your attempt was wrong, you'll understand the solution much better than if you'd just read it passively.
When Practicing Problems
Don't keep your notes open "just in case." Close them.
Yes, you'll get more wrong. Yes, it'll feel frustrating. But every time you struggle to remember a formula or method, you're strengthening your memory of it.
If you genuinely can't proceed, give yourself the smallest possible hint, then close your notes again.
When Something Feels Too Easy
If you're getting everything right during practice, something is wrong:
- Are the questions too easy? Find harder ones.
- Are you doing blocked practice? Mix in other topics.
- Are your notes open? Close them.
- Did you just study this? Leave a gap before practicing.
Some struggle is the goal. Chase it.
Finding the Right Level
Not all difficulty is desirable. The challenge needs to be in the right zone:
| Too Easy | Just Right | Too Hard |
|---|---|---|
| Getting everything right | Getting 60-80% right | Getting almost nothing right |
| No mental effort | Has to think carefully | Completely lost |
| Feels boring | Feels challenging but achievable | Feels impossible |
| Not learning much | Learning efficiently | Getting frustrated, giving up |
The sweet spot: You should be getting things wrong sometimes, but not so often that you can't learn from your mistakes.
Signs You're in the Right Zone
- You have to think before answering
- You make some mistakes but can understand why
- It feels effortful but not impossible
- You're slightly uncertain about your answers
- Time passes without you noticing (you're engaged)
Signs It's Too Easy
- You're on autopilot
- Everything feels obvious
- You're rushing through
- You feel confident about everything
- You're bored
Signs It's Too Hard
- You can't even start most problems
- You don't understand the solutions when you see them
- You're guessing randomly
- You feel anxious and overwhelmed
- You want to give up
Productive Struggle vs Unproductive Struggle
There's a difference between:
Productive struggle: "I'm not sure how to approach this... let me think... maybe if I try this method... no, that doesn't work... what about...?"
Unproductive struggle: "I have absolutely no idea what any of this means. I don't even know where to start. This is impossible."
Productive struggle means you're working at the edge of your current ability. Unproductive struggle means you're missing prerequisite knowledge.
If you're unproductively struggling with a topic, you probably need to go back and learn something more fundamental first. For example:
- Struggling with quadratic equations? Check you can expand brackets and solve linear equations first.
- Struggling with trigonometry? Make sure you're solid on Pythagoras and basic algebra.
- Struggling with histograms? Ensure you understand frequency and class intervals.
Reframing Difficulty
Try changing how you think about struggle:
| Instead of Thinking... | Try Thinking... |
|---|---|
| "I'm getting these wrong, I must be bad at this" | "I'm getting these wrong, which means I'm learning" |
| "This is too hard" | "This is challenging, which is what I need" |
| "I should find easier questions" | "These hard questions are more valuable" |
| "I don't feel confident" | "Confidence during practice doesn't predict exam success" |
| "This revision isn't working" | "This feels hard, so it probably is working" |
The discomfort is not a sign to stop. It's a sign that your brain is being challenged — which is exactly what builds stronger learning.
Quick Wins
Here are simple ways to add desirable difficulty to your revision today:
- Close your notes before attempting practice questions
- Wait a day before reviewing something you just learned
- Mix two topics in your next practice session
- Try the problem first before reading the worked example
- Explain your reasoning out loud as you solve problems
Each of these makes revision feel harder. Each of these makes revision work better.
The bottom line: If revision feels comfortable, you're probably wasting your time. Seek out the struggle — that's where the learning happens.
Related strategies:
- 🧪 Retrieval Practice — Testing yourself is desirable difficulty
- 🔄 Spaced Repetition — Spacing creates desirable difficulty
- 🔀 Interleaving — Mixing topics creates desirable difficulty
- 🔍 Elaborative Interrogation — Asking "why" deepens understanding