What is interleaved learning?

While many learning designers are familiar with the benefits of spaced repetition to encourage practice, over time, that facilitates mastery and retention of new knowledge and skills, the idea of interleaved learning might be a tougher sell. That’s because many people assume or “know” that you have to practice one skill at a time to get good at it, a practice called “blocking.”

They may be conflating instructional scaffolding with “practice makes perfect.” While it’s true that learners need to understand fundamental concepts before they can tackle more complex material, that does not mean they can’t be exposed to more than one foundational concept at a time.

Interleaving is a learning approach that mixes multiple related concepts: “For instance, a pianist alternates practice between scales, chords, and arpeggios, while a tennis player alternates practice between forehands, backhands, and volleys,” a Scientific American article said.

Researcher Doug Rohrer verified that students learning mathematics using interleaved problem sets outperformed students using more conventional problem sets that covered only a single concept (blocked practice) — and that they retained or increased their edge over several weeks.

Interleaving introduces desirable difficulty

The concept of “desirable difficulty” says that “introducing manipulations that make performance more difficult during practice” might improve long-term retention, according to Lin et al.

The desirable difficulty introduced in interleaved mathematics practice, according to Rohrer, is that students need to not only solve the problems, they must choose a strategy for each problem. Blocked practice, in contrast, removes that choice — all problems relate to the concept or strategy just studied.

Choosing a strategy requires figuring out what kind of problem each one is and then selecting the appropriate method of solving it, Roher wrote. “The choice of an appropriate strategy is often difficult because superficially similar problems sometimes require different strategies,” he added.

More realistic practice

While interleaving problems of different types does make practice more difficult, and therefore can impair performance, it also appears to improve long-term retention and learning transfer. That’s because, by asking that learners both choose the strategy and correctly apply it, interleaved practice more closely resembles real life — or final exams.

Researchers Robert and Elizabeth Bjork suggest three additional reasons for the effectiveness of interleaved learning:

• Interleaving evokes “contrasts and comparisons” that lead to more distinctive processing of the problems and solutions — which enhances retention and transfer.
• During blocked practice, opportunities for learners to forget and reconstruct solutions are minimal; interleaved practice provides spaced practice in recalling and applying a variety of solutions.
• Interleaving draws learners’ attention to the features that distinguish different types of problems and their solutions.

Interleaving and spaced practice are natural allies

Interleaved learning naturally reaps the proven benefits of spaced repetition. Rather than learning a concept, practicing only that concept, and moving on, learners encounter the new material as well as all previously learned concepts repeatedly in learning sessions. Thus they are organically engaging with content over and over again throughout a term or the lifespan of their learning program.