19 December 2025 · Updated 13 August 2026 · Hugo Harrabin
Revising one topic at a time feels organised and produces worse exam results. Here's what mixing topics does instead, and how to start.
Ask a GCSE student how they revise maths and you'll usually hear the same thing. All the algebra first, then all the geometry, then trigonometry. Topic by topic, block by block.
It feels organised, and that's the problem. Working through one topic at a time means your child never practises the thing the exam actually asks of them: working out which method a question needs when nothing on the page tells them.
Key Takeaways
- Revising one topic at a time is called blocked practice. Mixing topics within a session is interleaving.
- In a classroom study of seventh-grade maths, mixed practice beat blocked practice by 16 points on a test a day later and by 32 points a month later. Same problems, same total practice, different order.
- Blocked practice hides the hardest step. When every question is algebra, your child never has to work out that it's algebra.
- It feels worse. Students finish a mixed session less confident than after a blocked one, and that's expected rather than a warning sign.
- Interleaving sets what order your child revises in. It sits alongside when they revise and whether the revision is active, which are separate decisions.
Mixing different topics or question types inside one revision session, instead of finishing all of one type before starting the next.
A blocked maths session looks like this: ten algebra questions, then ten trigonometry questions, then ten probability questions.
An interleaved session covers the same ground in a different order: algebra, trigonometry, probability, algebra, probability, trigonometry, jumbled all the way through.
Same questions. Same amount of time. The only thing that changes is the order, and the order turns out to matter a great deal.
It does, and the clearest evidence comes from an actual classroom rather than a lab. Rohrer, Dedrick and Stershic (2015) gave seventh-grade maths students the same practice problems across three months. For some students the problems were blocked by topic in the usual way. For others the identical problems were mixed together. Then they tested them, once a day after a review session and once thirty days after.
A day later the mixed group was 16 points ahead. A month later the gap had doubled to 32 points. The reason is visible in the shape: the mixed group barely dropped, from 80% to 74%, while the blocked group fell off a cliff, from 64% to 42%. The authors describe mixed practice as giving "near immunity against forgetting."
The earlier study that started this line of work found the same reversal in a different way. Rohrer and Taylor (2007) had students practise maths problems either blocked or shuffled. Blocked practice looked better during the practice session itself. A week later, the shuffled group was well ahead. Blocked practice buys confidence in the moment, but falls apart later.
When your child does twenty algebra questions in a row, they never have to decide which technique to use. The format has already told them. They're practising the technique but skipping the harder skill sitting in front of it: recognising what kind of problem this is.
I've watched this happen in a classroom. Give a class ten of the same type of question in a row and at some point they stop solving them. They copy the shape of their own previous answer and change the numbers. The page fills up with correct working, which is what makes it so easy to miss, but the thinking has quietly stopped and nothing is being pulled back out of memory any more. What looks like ten questions of practice is closer to one question and nine copies.
GCSE papers don't group questions by topic. A maths paper might run a probability question, then vectors, then simultaneous equations, in any order. A student who has only ever practised in blocks has to do something in the exam hall they have never once rehearsed, which is identify the method from the question itself. Plenty can't, and it reads as not knowing the topic when it's actually not recognising it.
Interleaving drills exactly that step. Every question starts with a beat of what is this one? That beat is the whole point.
It also explains why interleaving helps most in subjects where methods look similar and get confused with each other. Mixing forces your child to notice the difference between a question that needs the sine rule and one that needs Pythagoras, rather than assuming, correctly, that everything on this page is Pythagoras.
Because it is going slower, and that's the trade. Revision should feel like hard work.
After a blocked session on trigonometry your child feels fluent. After a mixed session they feel scattered and unsure they've mastered anything. That feeling is closer to the truth: it reflects how well they'd cope with a real paper. The fluent feeling after blocked practice reflects how well they'd cope with another page of trigonometry, which is not what they'll be sitting in their GCSE exam.
This is worth explaining to them directly, because otherwise the method that's working feels like the method that's failing, and it gets dropped after one session. Confidence during revision is a poor guide to readiness, for reasons that go beyond interleaving.
A Quick Test for Students: after a blocked session on, say, trigonometry, shuffle questions from your last three maths topics and answer them mixed together. If your score drops a lot, that gap is the useful information. You'd built familiarity with the format rather than command of the methods.
Four changes, none of which need new materials:
| Instead of | Do this | Why |
|---|---|---|
| Working through one topic per session | Rotate between three or four topics in the same session | Forces the recognition step every question |
| Reading the topic heading first | Cover the heading and work out the method yourself | The heading does the hardest part for them |
| Revision cards grouped by topic | Shuffle the deck across topics | Same cards, harder and more useful retrieval |
| One science module per session | Mix questions from different modules | Exam papers mix modules, so practice should |
For essay subjects the same idea applies: alternate between questions on different texts or periods rather than spending the session on one.
One caution. Interleaving works when your child broadly knows the methods and needs to tell them apart. If a topic has genuinely never been understood, mixing it in early just produces four topics of confusion instead of one. Teach it first, then mix it.
Interleaving is the second pillar of the Tugo Method. Rather than spending a session on a single topic, tutors deliberately rotate between topics, so students keep meeting the question they can't predict.
It's also the pillar students are least likely to adopt alone, because it requires deliberately making revision feel worse. A tutor setting the order removes that decision, which is most of the battle.
Mixing different topics or question types within one study session instead of finishing all practice on one topic before moving on. It feels harder than working through topics in blocks and consistently produces better results on tests taken days or weeks later.
For exam performance, yes. Blocked practice produces better recall immediately after the session, and worse recall by the time the exam arrives. In the classroom study above the advantage of mixing grew from 16 points at one day to 32 points at thirty days. Since GCSEs are sat weeks or months after most revision, the delayed figure is the one that matters.
Only if they haven't learned the topics yet. Interleaving trains your child to tell methods apart, which needs them to know the methods first. Once a topic has been taught properly, the confusion of mixing is the useful kind. Before that, it isn't.
Anything where methods can be mistaken for each other. Maths and the sciences benefit most, because a question that looks like one method often needs another. It works for essay subjects too, though the gain is smaller, since choosing an approach there is less of a single identifiable step.
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