7 – Interleaving Theory

We acquire language when we interleave its retrieval.

In the previous two chapters, we looked at Retrieval and Spacing Theory. Briefly, let’s review. With retrieval, we recall facts, concepts, events, words, phrases, and grammatical bits from memory. We can do retrieval in receptive and productive ways. We know that this works better than reviewing notes or re-reading textbooks (Brown & McDaniel, 2014). And we know that self-quizzing is an effective way to practice retrieval.

With spacing, we open a space of time between retrieval sessions. During the space, we start to forget. Because we start to forget, we find it harder to retrieve information from memory. Therefore, we must make more effort, but with the extra effort, we get a benefit. We learn better. We remember more. We remember longer.

With spacing and retrieval, we can add another challenge. It’s called interleaving. With interleaving, we mix different but related topics or subjects. We can compare interleaving with traditional study, which is called “blocking.” With blocking, we practice one skill at a time. Practice Skill X. Then practice Skill Y. Then practice Skill Z. Blocked practice looks like this. XXX-YYY-ZZZ.

But with interleaving, we mix and shuffle the practice of XYZ, so practice sessions look like this: XYZ-XYZ-XYZ. When we interleave practice, we find it harder to retrieve information. We add the challenge of spacing (and forgetting) with another challenge of interleaving. Now we need more effort to retrieve after spacing and with interleaving. With more effort, we get a benefit. We learn better. We remember more. We remember longer.

However, when we do retrieval with spacing and interleaving, we need to remember something. The extra effort feels less productive. We feel like we are starting too slowly. This is because we start to forget (after spacing) and because spacing and interleaving require more work. But we get benefits from the extra work. With massed practice (no spacing; no interleaving), we may remember for the short term. But with retrieval, spacing, and interleaving, we are more likely to remember for the long term.

What about interleaving and language learning? Of course, we can do retrieval, spacing, and interleaving with word cards. But how does interleaving work with grammar? For grammar, teachers tend to focus on one grammar point at a time. But in the real world, we don’t hear, read, speak, or write with only one grammar point at a time. Input and output of grammar is interleaved. Thus, ideally teachers need to interleave grammar points in their grammar lessons.

But we can also naturally experience interleaving with extensive reading. With extensive reading, we meet grammar rules, words with rules, and phrases with rules. And all this language is interleaved naturally in texts. Thus, when we do extensive reading, we do receptive retrieval with the spaced repetition and interleaving of grammatical and lexical information. That is, when we get natural language input through extensive reading (or listening), the power of receptive retrieval, spaced-repetition, and interleaving work for us.


Dr. Joseph Poulshock

Dr. Joseph Poulshock is a professor of English linguistics in the Faculty of Economics at Senshu University.