Interleaving: Why Mixing Topics Helps You Study

Most textbooks are organized in blocks: a chapter on one method, then twenty practice problems that all use that method. By problem five you already know the method before you read the question. An exam doesn't tell you which chapter a question comes from. Interleaving practices that missing step, figuring out what kind of problem you're looking at, by mixing problem types together during review.

What the research says

Interleaved practice has been studied most in math and in learning to tell categories apart, like matching paintings to artists or identifying types of problems. A widely cited 2013 review of study techniques by Dunlosky and colleagues rated interleaving as moderately useful. It was promising, especially for problem solving, but tested in fewer subjects than practice testing or spaced practice. The pattern across studies is consistent: interleaving makes practice feel harder and go less smoothly, and leads to better results on later tests.

How to interleave your own practice

1. Learn each topic first with blocked practice. Interleaving is for review, not for meeting a method for the first time.
2. Once you've covered two or three related topics, mix their problems together in one set.
3. Before solving each problem, name the method or concept it needs. That decision is the skill you're training.
4. Keep the topics related. Mixing derivatives with integrals helps; mixing calculus with French vocabulary doesn't add much.
5. Expect more mistakes at first. That's the method working, not a sign it isn't.

Interleaving vs. spaced repetition

They're related but different. Spaced repetition is about when you review: spreading reviews of the same material over days. Interleaving is about what goes in one session: mixing different material together. They work well together: a review session that mixes several earlier topics is both spaced and interleaved.

Using it with Studi

The hard part of interleaving on your own is getting mixed practice at all, because textbook problem sets are blocked by chapter. In Studi, upload the material for several units, like a few lecture decks or chapters, and generate a practice test from all of it together. The questions come from across the topics, so you have to work out which concept each one is asking about. Studi also varies the question types as you go, so you don't get long runs of the same format.