Short answer
Blocked practice repeats one announced problem type before moving to the next. Interleaved practice mixes related types so you must first decide which method applies. That extra choice can reduce accuracy during practice while improving later selection of the right procedure. Use it after the underlying methods have been introduced, and mix confusable, related problems rather than switching randomly among unrelated subjects.
What to remember
- Ease during practice is not the same as independent performance later.
- Interleaving is most relevant when choosing the method is part of the task.
- Mix related, already-introduced problem types instead of randomizing everything.
- Review whether an error came from choosing the wrong method or executing it poorly.
Blocked and interleaved practice train different decisions
In a blocked worksheet, the section heading often tells you what to do: solve ten problems using the same formula, then move to a new formula. You still practice execution, but the page makes the method-selection decision for you.
An interleaved set removes that label and mixes a small number of related problem types. Before calculating, you have to notice the cues, retrieve the available methods, and choose one. That selection step is part of many exams and real tasks, even though it makes the practice session feel less smooth.
Why harder practice can produce a better delayed test
In a classroom mathematics experiment by Taylor and Rohrer, students practiced four problem types either in blocks or in an interleaved order. The interleaved group performed worse during practice but substantially better on a test one day later. The authors connected the advantage to learning how to discriminate among problem types.
That result is specific to the students, mathematics tasks, schedule, and test in the experiment. It does not mean every subject should be shuffled. It does show why immediate completion rates can be a misleading measure when the later task requires deciding what kind of problem you are facing.
A 30-minute mixed-practice session
Refresh one worked example
Spend five minutes on one already-taught problem type. Cover the solution and name the cue that tells you which method applies.
Solve two related problems
Use the method twice with feedback available afterward. If the procedure itself is still unfamiliar, stay here before adding more types.
Introduce one confusable type
Add a problem that looks similar but requires a different method. Write the deciding cue before solving it.
Finish with an unlabeled mini-test
Mix four to six questions from the small set. Do not label the method. Check both the choice and the execution when you review.
Run a one-week experiment on your own material
- Choose two or three related problem types that have already been explained.
- Use a blocked set on one day and a mixed set on another day.
- Keep the number and difficulty of problems roughly comparable.
- After a delay, take one unlabeled mixed quiz without notes.
- Record method-selection errors separately from calculation or syntax errors.
Common questions
Is interleaving the same as switching between unrelated subjects?
No. The useful comparison here is among related skills or problem types whose cues must be distinguished. Randomly switching among unrelated tasks may add interruption without training that decision.
Should beginners interleave immediately?
Introduce the underlying methods first. A learner who cannot yet execute either method may need worked examples and short blocked practice before a mixed set becomes informative.
Does interleaving replace spaced repetition?
No. Interleaving changes the order of related items within practice; spacing changes when practice returns over time. A study plan can use both.
Sources and method
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- Institute of Education Sciences: Organizing Instruction and StudyOfficial practice guide recommending an alternating sequence of worked examples and problems to solve.
- Taylor and Rohrer (2010), Applied Cognitive PsychologyOriginal classroom experiment comparing blocked and interleaved mathematics practice.
