Interleaving: Why Mixing Topics Can Help You Learn
Interleaving means mixing different topics or problem types inside one study session instead of finishing one topic before starting the next. By the end of this guide you will know what the main studies on it found, why it tends to feel worse while you do it, and how to mix your own cards or problem sets.
The evidence here is thinner than for spacing or self-testing: a large review gave interleaving only a moderate rating, mainly because the evidence was still thin when it was written. We point out where the studies stop so you can judge how far to trust the idea.
A quick vocabulary note. Studying one type of item in a row is called blocked practice. Spreading study over several days is spacing. The two are different levers, and this guide is about the first one.
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Blocked versus interleaved: the same items in two orders
Say you are practicing three kinds of math problems: percent change, ratios and unit conversion. Blocked practice does all the percent problems, then all the ratio problems. Interleaved practice rotates through the three kinds. You solve the same number of problems either way, and only the order changes.
| Feature | Blocked | Interleaved |
|---|---|---|
| Order of six problems | Percent, percent, ratio, ratio, unit, unit | Percent, ratio, unit, percent, ratio, unit |
| What you must decide | Little: the last problem used the same method | Which type is this, before you solve it |
| How it feels | Smooth, with quick early progress | Slower and more effortful |
| Main risk | Feeling sure because the method is still fresh | Feeling discouraged and switching back |
What the studies found
Two laboratory studies carry most of this guide. In the first, college students practiced math problems. In one experiment, problems randomly mixed across types led to far better performance one week later than problems blocked by type. A separate experiment, on spacing, also favored practice spread over several sessions (Rohrer and Taylor, 2007). The authors also compared a shuffled format, used in a small number of textbooks, with the standard format and found the shuffled one better in both experiments.
The second study used paintings instead of math. Participants studied paintings by different artists, then tried to identify which artist painted new paintings. Mixing the artists beat showing each artist's paintings in a row. Participants nonetheless rated the blocked study as more effective, even after their own test results showed the opposite (Kornell and Bjork, 2008). In that paper, mixing counts as spacing, since other paintings sit between two by the same artist. The paper reports that spacing can help learning of concepts and categories, not only recall of single facts.
The large study-techniques review mentioned earlier gave interleaved practice a moderate utility rating, and the thin evidence at the time was the main reason (Dunlosky et al., 2013). Its high ratings went to practice testing and spacing.
Why it feels harder, and where it stops helping
Bjork and Bjork list interleaving instruction on separate topics among the desirable difficulties, meaning study conditions that feel harder yet can support longer-lasting learning (Bjork and Bjork, 2011). They also argue that current performance can be a misleading index of learning, because conditions that make performance improve quickly often fail to support long-term retention. Our reading is that blocked practice can look like that kind of quick progress while the session is running.
The same chapter adds a limit that matters: many difficulties are undesirable, and a difficulty is desirable only when the learner has the background knowledge or skills to respond to it. Our reading is that you should not interleave material you have not met yet.
Other limits are plain. Both studies were laboratory experiments with specific materials, and painting styles do not transfer directly to vocabulary lists or definitions. The math study tested one-week delays and separated mixing from spacing. We found no verified study that tells you how much to mix, so any ratio is a guess you should test yourself. Results vary between people.
How to mix your own cards or problem sets
The steps below are practical advice built on the studies above. The specific steps have not been tested in those studies.
- Learn each topic once first, with notes or a worked example, so the mixed practice has something to work on.
- Shuffle related topics together in one session. In Practice, the deck menu has an All decks option, and cards inside a session are shuffled.
- For problem sets, build a mixed page: two problems from each of three chapters, in scrambled order.
- Before you solve, name the type of problem or the rule you need. Telling the types apart is the extra step that mixed practice adds.
- Keep the mix related, so that the topics could plausibly be confused.
Interleaving fits well with a weekly rhythm. The weekly review plan has a template with a mixed-practice day, the daily review habit guide helps you keep sessions small, and the study session length guide helps you size a mixed session. For formulas in particular, see memorizing math formulas, and for the timing side of the story, compare spaced practice vs. cramming. To try a shuffled session, open the Practice trainer and choose All decks.
Common mistakes
- Interleaving topics you have not learned yet. Study each topic once on its own first. A difficulty helps only when you have the background to respond to it.
- Judging the method by how smooth the session feels. Blocked practice feels smooth, and in one study people rated it as more effective even after their results showed the opposite. Check yourself with a delayed test instead.
- Mixing unrelated subjects and expecting the same effect. The studies mixed related types, such as kinds of math problems or artists. Mix topics that you could confuse.
- Confusing interleaving with spacing. Spacing is about gaps in time, and interleaving is about the order of topics. You can use both, but the studies tested them separately.
Frequently asked questions
What is the difference between interleaving and spacing?
Spacing puts time between repeated study of the same material. Interleaving mixes different topics or problem types within a session. Kornell and Bjork treated mixing as a form of spacing, since other items sit between two from the same category, but the math study tested the two ideas in separate experiments.
Does interleaving work for vocabulary or definitions?
We found no verified study that tests it there. The cited studies used math problems and paintings. Shuffling decks is easy to try, so you can run a small test on yourself and compare results after a delay.
How much should I mix?
No verified source gives a ratio. A practical start is to rotate among a few related topics in a session, then see whether your delayed results improve. Treat that start as our suggestion.
Will interleaving raise my grades?
We cannot promise that. The studies measured later performance on specific tasks in laboratory settings. Whether it helps in your course depends on the material, your starting knowledge and how you practice.
Sources
We opened each source below before citing it. See Methodology and Sources for how we check them.
- Rohrer, D., & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35(6), 481-498. Open the source
- Kornell, N., & Bjork, R. A. (2008). Learning concepts and categories: Is spacing the 'enemy of induction'?. Psychological Science, 19(6), 585-592. Open the source
- Bjork, E. L., & Bjork, R. A. (2011). Making things hard on yourself, but in a good way: Creating desirable difficulties to enhance learning. In Psychology and the Real World: Essays Illustrating Fundamental Contributions to Society (Worth Publishers), pp. 56-64. Open the source
- Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving Students' Learning With Effective Learning Techniques: Promising Directions From Cognitive and Educational Psychology. Psychological Science in the Public Interest, 14(1), 4-58. Open the source
This guide is general study help, not medical or professional advice. It was last reviewed on November 12, 2026. Spot a mistake? Tell us here.