What is interleaving in studying with examples?
Key takeaways
- Interleaving means mixing different topics or problem types in one study session instead of studying them one at a time.
- In a 787-student trial, interleaved students scored 61% versus 38% for blocked students on a delayed test.
- It feels harder during practice but produces stronger long-term memory and better transfer to new problems.
Interleaving is a study method where you mix different topics or problem types in one session instead of finishing one topic before moving to the next. Doing one topic at a time is called blocking, says cognitive scientist Rick Bryck, PhD, writing for Landmark College.
It feels backwards. If you are studying math, your instinct says to do twenty slope problems, then twenty graphing problems.
Interleaving says to shuffle them: slope, graph, slope, graph. The research says the shuffle wins.
This article explains what interleaving is, what the research shows compared with blocked study, worked examples across subjects, how to interleave your own sessions, and when the method is less useful.
What is interleaving?
Interleaving means alternating between types of information, whether subject areas, topics, or problem types, instead of handling them one at a time, in Bryck's definition. Blocking is the intuitive and much more common one: one topic at a time, in a straight sequence.
To see the difference, picture two students studying for a math test with four problem types. The blocked student does all the slope problems, then all the graphing problems, then all the linear equations, then all the quadratics.
The interleaved student shuffles the same problems into a mixed deck. Same problems, same total study time, different order.
Researchers call interleaving a "desirable difficulty," a phrase coined by Robert Bjork in 1994. Desirable difficulties make learning feel harder in the short term but improve recall in the long term. During practice, blocked students usually look better. They solve problem after problem correctly and feel confident.
On a later test, the advantage flips, and the interleavers pull ahead.
Why does mixing work? Bryck points to two likely mechanisms. First, interleaving forces you to choose a strategy on every problem instead of repeating the same one, which builds stronger discrimination between problem types.
Second, alternating topics forces retrieval of the right method from long-term memory each time, while blocked practice lets the current rule sit comfortably in working memory.
Each switch is a mini test, and testing is one of the best-documented ways to strengthen memory.
Interleaving vs blocking: what the research shows
The evidence for interleaving is unusually consistent across labs, ages, and materials. Here are the key studies, in order.
The starting point is Rohrer and Taylor (2007), published in Instructional Science, who had college students practice volume formulas in blocked or interleaved order. During practice, the blocked group solved nearly every problem correctly. On a test one week later, the advantage reversed: the interleaved students dramatically outperformed the blocked students, according to a review by Glasp.
Then came real classrooms. Taylor and Rohrer (2010) had fourth graders practice four kinds of math problems.
One day later, the interleaved group scored 77% against 38% for the blocked group, an effect size of d = 1.21, Glasp reports. Interleaving roughly doubled the score.
Rohrer, Dedrick, and Stershic (2015) ran 126 seventh graders over three months and published in the Journal of Educational Psychology. The interleaved advantage on a delayed test reached d = 0.79. Most striking: when the delay before testing grew thirty-fold, blocked students' scores collapsed while interleaved students' scores slipped only from 80% to 74%. Interleaving made the learning nearly immune to forgetting, Glasp's review notes.
The capstone trial is Rohrer, Dedrick, Hartwig, and Cheung (2020), published in the Journal of Educational Psychology: a randomized controlled trial with 787 students across 54 classes in five schools. Students practiced interleaved or blocked assignments over four months, then took an unannounced test one month later. The interleaved students scored 61% versus 38%, with a large effect size of d = 0.83.
The effect is not limited to math. In an early motor-skills study, baseball batters practiced hitting fastballs, curves, and change-ups in blocked or random order; at a test with pitches delivered in game-like random sequence, the interleaved group got more hits, according to Hall, Domingues, and Cavazos (1994), cited by Bryck. Badminton players showed the same pattern for three serve types in a 1984 study by Goode and Magill, cited by Bjork and Bjork (2019).
In 2003, one of the first studies outside sports found that interleaving helped medical students make more accurate electrocardiogram diagnoses than blocking, Scientific American reports. In 2008, college students learned to recognize landscape painters' styles better with interleaved examples. In 2011, students trained with interleaving made more accurate assessments of complex legal scenarios.
Music students identified musical styles faster with interleaved practice, according to a 2011 study by Simmons.
Be honest about the strength of the evidence, though. Bryck notes that the strongest and most robust effects so far are in mathematics.
Not every study has shown a statistical benefit over blocking. Interleaving is a genuinely promising technique, but it is not magic.
Examples of interleaving in different subjects
The principle is simple: mix, don't block. Here is what it looks like in practice.
Math. Instead of a worksheet of 20 factoring problems, build a set with 5 factoring, 5 quadratic equations, 5 graphing, and 5 word problems, then shuffle. This mirrors Rohrer and Dedrick's 2015 setup with 126 seventh graders, where students worked on graphing linear equations and finding slopes in mixed order. You must identify the problem type before solving, which is exactly the skill exams test.
Science. Alternate between balancing chemical equations, predicting reaction types, and naming compounds in one session. Bryck notes that interleaving works even when problem types look quite different, such as proportions, linear equations, and graphing within math, according to Rohrer et al. (2015).
Languages. Mix vocabulary, grammar drills, and listening in one session rather than doing a full hour of vocabulary first. One caveat from Scientific American: with a completely unfamiliar language, interleaving has produced mixed results. When native English speakers learned English-to-Swahili translations, interleaving sometimes helped and sometimes hurt. The lesson: get some familiarity with the material first, then interleave.
Music. Practice three pieces or styles in rotation instead of perfecting one before touching the next. Simmons (2011) found this helped music students recognize styles faster.
Sports. A badminton player should practice long, short, and drive serves in mixed order, and a baseball player should face mixed pitch types in the batting cage. This is where interleaving was first demonstrated, and the game-like randomness of the test matches how performance actually works.
Art and classification. Medical students diagnosing ECGs and students learning painters' styles both benefited from interleaved examples, Scientific American reports. When you must tell similar-looking things apart, mixing trains your eye to notice the differences.
The thread connecting all of these: interleaving trains the "which method do I use?" decision, which blocked practice never forces you to make.
How to interleave your own study sessions
You do not need to change what you study, only the order. Here is a practical setup.
Step 1: collect problem types. List the 3 to 5 distinct skills or topics your exam will test. For a biology test, that might be cell division, genetics crosses, and ecological cycles.
Step 2: build a mixed set. Take a few problems from each type and shuffle them.
Step 3: label before you solve. For each problem, first name which type it is and which method it needs, then solve. This "identify, then solve" habit is the active ingredient.
Step 4: space the sessions. Interleaving pairs well with spaced practice, another desirable difficulty backed by many classroom studies, according to Bryck. Two mixed sessions a week apart beat one long mixed session.
Step 5: expect it to feel bad. Your practice scores will drop compared with blocked practice. That is normal and predicted by the research. Judge the method by test scores a week later, not by how smooth the session feels.
A concrete weekly plan for a math student: Monday, do 15 shuffled problems from chapters 3 and 4. Wednesday, do 15 shuffled problems from chapters 4 and 5. Friday, do 10 problems shuffled across chapters 3, 4, and 5.
Interleaving also combines well with other evidence-based habits: reading textbooks for structure instead of highlighting, testing yourself rather than rereading, and handwriting notes to force retrieval.
When interleaving is less useful
Interleaving is not always the right first move. Two honest limits from the research.
First, if you have never seen the material, learn the basics in blocked form first. Bryck notes that open questions remain about how much initial blocked practice should come before interleaving. The foreign-language results reported by Scientific American show that interleaving totally unfamiliar material can confuse more than it helps.
Get the concepts down, then mix.
Second, interleaving is underexamined in some populations. Bryck points out that studies with students who have learning differences are still lacking, and research is underway at Landmark College on exactly this. If interleaving feels unmanageable for a particular subject, a mix of blocked-then-interleaved is a reasonable compromise.
Also keep perspective on what interleaving cannot fix. It will not rescue cramming the night before an exam, and it cannot replace understanding. If the underlying concepts are missing, shuffling problem order only shuffles confusion.
Frequently asked questions
Is interleaving better than blocking for all subjects?
The evidence is strongest in math, with large effect sizes in classroom trials of 126 and 787 students. Benefits also appear in sports, music, art recognition, and medical diagnosis. Results are mixed for completely unfamiliar foreign-language material.
Why does interleaving feel worse during practice?
Because blocked practice lets you reuse the same method on autopilot, so practice scores look great. Interleaving forces you to retrieve the right method each time, which feels slower. Robert Bjork's "desirable difficulties" idea says this short-term struggle is exactly what builds long-term memory, according to Bryck.
How much should I interleave?
Research has not settled the optimal ratio or schedule. A practical rule: mix problem types within a session, and mix sessions across topics over the week. Start with a short blocked warm-up on new material, then switch to interleaved practice, as Bryck suggests is an open but reasonable approach.
Does interleaving help with exam anxiety?
No study in this literature measures anxiety directly. But interleaving makes practice feel like a test, with mixed, unpredictable questions.
Students often report that the real exam then feels more familiar. Pair it with keeping distractions like your phone under control for calmer sessions.
The bottom line
Interleaving means mixing different topics in one study session instead of blocking them. Classroom trials with hundreds of students show it roughly doubles delayed-test scores in math, and the pattern holds across sports, music, and medicine.
It will feel harder than blocking, and that is the point. Try one shuffled problem set this week and compare your recall seven days later. To review the contrast with fast-reading study methods, see the difference between skimming and scanning.
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