Many people don’t know how to practice effectively. Even some of the most talented people in the world could use tips on how to practice, especially when it comes to what’s known as interleaving. 

Take, for example, soccer champ Cristian Ronaldo. Like many pros, his intense training involves repetitions of drills. First, we see his knee dribble, on repeat. Then, he practices short passes, one after another. Followed by repetitions of headers, then cut-backs, over and over, then sprinting reps.

This repetitive practice sequence, while popular among star athletes, is not actually supported by research, which suggests that there is more benefit from variation in practice rather than repetition. In other words, to maximize his practice time, Ronaldo should alternate his moves: a cut back followed by a short pass, then a knee dribble, a header, and switch to sprinting.

This idea of mixing it up, or ”interleaving”, is a simple and effective way to boost the learning potential. The interleaving process optimizes learning, increases long-term retention and helps refine the ability to build on knowledge to solve problems and master new concepts.

For example, when learning a language, instead of doing 10 vocab drills, 10 verb conjugations, and 10 subject-verb agreement, alternating the exercises allow learners to find patterns and make connections between the different activities. In a more effective lesson, students would do a vocab exercise, followed by a verb conjugation, then a subject-verb agreement problem. Using this process, students are able to recall known strategies and identify and apply the most effective one to solve new problems. In essence, interleaving helps you avoid repeating mistakes by constantly resurfacing past knowledge.

Interleaving Is Effective

A wealth of research offers insight into the value of interleaving as a learning strategy. In a study from the 1990s that observed young women who learned to fire off foul shots, there were women who practiced only foul shots, and other women took more of a non-traditional approach; they practiced foul shots as well as eight and fifteen footers in tandem. This strategy of “mixing it up” brought outstanding results. The non-traditional group performed significantly better and demonstrated a more in depth understanding of the underlying concept. 

Interleaving also applies to academic fields. Interworking different examples in succession results in a more robust understanding of what lies underneath the surface. This practice also allows for a more well-rounded sense of the system. The lesson is this: vary your practice—and avoid repetition. 

“The ultimate crime is practicing the same thing multiple times in a row. Avoid it like the plague,” said psychologist Nate Kornell. A much more effective strategy is to “practice for a long chunk of time but don’t repeat anything.”

Imagine you’re studying astronomy. You’ve been assigned to read two articles each about planetary evolution, solar science, and astrophysics. What is the best way to master this subject? Mix up your reading. Read a planet article, then astrophysics, then read about the sun. Rinse and repeat.

Interleaving also applies to academic fields. Interworking different examples in succession results in a more robust understanding of what lies underneath the surface.

Why Does Interleaving Work?

Interleaving works because it involves a more effective style of practice. On the opposite end of the spectrum is “blocked practice,” which requires no variation and  instead focuses on the repetition of only one skill. In other words, drills. In blocked practice, students repeat the same approach over and over to solve the same type of problem like, well, Ronaldo. They’re never challenged to build on what they have learned to decide which strategy or procedure to apply to each problem. Importantly, interleaved practice helps students associate the right strategy with the right problem.

This style of learning may be more demanding but it produces significant long-term impacts on students overall educational development. To be clear, research doesn’t suggest that blocked is never useful. In fact, in the early stages of the learning process, blocked practice is often necessary.

Think of students learning The Pythagorean Theorem in math class. To demonstrate understanding of the concept, students need to not only apply the equation but also recognize problems that can be solved through its application. Practicing these types of problems ensures the student will know what to do when they encounter a problem like this:

“What is the length of a diagonal of a rectangular picture whose sides are 12 inches by 17 inches?”

WIth few exceptions, mixing it up makes learning more active. Interleaved practice encourages retrieval by constantly switching up learning subjects, meaning every problem calls for a different strategy to solve than the last.

In the astronomy example, mixing the articles up helps the brain identify connections between different subjects, allowing for richer forms of learning and an overall better understanding of the issue at hand. Interleaving also strengthens associative memory, the ability to learn and remember the relationship between unrelated items.

Interleaving works because it allows you to forget some information and forces your brain to retrieve it while also highlighting the areas in your studies that need more attention. This process, called spacing or distributed practice, increases retrieval and maximizes the brain’s ability to store and keep important information long-term, which is highly beneficial come exam time.

While interleaving and distributed practice are two different types of learning interventions, the two go hand in hand because interleaving essentially introduces spacing. Distributed practice equals consistent revision, which is necessary to succeed in interleaving as well as retrieval practice.

In practice, interleaving often results in worse performance during the practice sessions, but far higher performance on subsequent tests and engagements.

Interleaving works because it allows you to forget some information and forces your brain to retrieve it while also highlighting the areas in your studies that need more attention.

Interleaving As A Way To Promote Critical Thinking

I learned the power of interleaving when I met with psychologist Robert Goldstone, at a coffee shop in downtown Washington. Goldstone, a professor at Indiana University Bloomington, sports a bald head on top of his tall frame.
“You seem like a smart guy,” Goldstone complimented me. “Can I put you on the spot?”
            “Sure,” I answered anxiously, waiting for his reply.  

Goldstone then revealed a scenario for me to solve that was similar to this one:
“An aging king plans to divide his kingdom among his daughters. Each country within the kingdom will be assigned to one of his daughters. (It is possible for multiple countries to be assigned to the same daughter.) In how many different ways can the countries be assigned, if there are five countries and seven daughters?”

After listening to Goldstone carefully, I jotted down the most important points, making sure to note the five countries and seven daughters. Then I thought it might help my thought process to draw it out, so I began to sketch out the provinces.

“Does it have something to do with factorials? That somehow seems familiar?” I said.
Goldstone scratched his neck, “You’re getting closer.”

I kept attempting the problem, working hard at a solution. 

“Can I give you a hint?” Goldstone asked. “If the king gives Germany to one daughter. He can still give France to the same daughter.”

I nodded my head, feigning understanding. Eventually, Goldstone gave in and explained:

“If there are seven options, or daughters, for each of the 5 things, or kingdoms, that need to be assigned to an option, there would be 7 X 7 X 7 X 7 X 7 or 7^5 possibilities.” 

What Goldstone was trying to convey was that the problem hinged on a math concept known as “sampling with replacement.” The topic is often taught in middle school as “The number of options raised to the power of the number of selections.”

So why did I get the answer wrong? To answer that question, we need to understand something else: what is the nature of a problem? According to psychologists like Goldstone, problems contain “surface” and “deep” features. Surface features are concrete and generally superficial, while deep features are typically concepts or skills.

In the king example, the kingdoms, daughters, and age of the king are the surface features. These things are concrete or “fixed” meaning they are factual and won’t change. According to Goldstone, the deep features are “the notion of sampling with replacement, the concept of an option, and the concept of a selection event.”

At that time, I couldn’t see the deep features since I was focused on the superficial ones. Goldstone argued that people often get distracted by the superficial. In his words, it is “the greatest cognitive difficulty.” Here is another example from Goldstone’s study:

“A homeowner is going to repaint several rooms in her house. She chooses one color of paint for the living room, one for the dining room, one for the family room, and so on. (It is possible for multiple rooms to be painted the same color or for a color never to be used.) In how many different ways can she paint the rooms, if there are 8 rooms and 3 colors?”

The concept of sampling with replacement is not immediately clear unless you are familiar with this type of problem. The fact that the problems have different superficial features but similar deep ones, is difficult to wrap one’s head around. “To see this connection you need to see the role that daughters and colors play in their respective scenarios–they are alternatives,” Goldstone argues.

​How does one conceptualize deep features in problems? A simple solution goes back to interleaving.  The practice of interleaving facilitates retrieval and engagement around systems and analogies. When people see multiple examples with different surface details, they’re far more likely to understand the underlying system.

According to psychologists like Goldstone, problems contain “surface” and “deep” features. Surface features are concrete and generally superficial, while deep features are typically concepts or skills

Interleaving In Classrooms

Not long ago, our team at the Learning Agency worked with teachers Kim Kelly and Shannon Payette at Sky View Middle School in Leominster, MA. They were teamed up with Dr. Megan Sumeracki, a learning scientist at Rhode Island College, to engage interleaving in the classroom.

Kim and Shannon set about the time-consuming task of modifying traditional learning materials that rely on blocked practice, to implement interleaved practice in their homework assignments and tests. Their hard work paid off, as they reported improvements in students’ ability to solve problems after the engaging interleaving in their classrooms. Kim noticed her students were more prone to “stopping and thinking…their brain had to shift from this topic back to some old material.”

Shannon also noticed improvements, particularly in one student who had previously struggled in math. “(He) did not meet expectations for math at all on his (state) test last year.” After the introduction of interlearing, he excelled in a practice standardized test. “He got 6 out of 6!”

Practically speaking, try incorporating a mixture of problem types and concepts learned throughout the school year into coursework, rather than assigning problems based on what they’ve just learned. As with Dr. Goldstone’s questions, this type of variation is particularly effective when problems have different superficial features but are based on similar concepts or strategies. By the same token, problems with similar surface features that require different strategies to solve allow for a distributed practice and an overall better understanding of underlying concepts.

“What interleaving does,” Dr. Sumeracki explains, “is force the students to figure out not just how but also when to use a specific problem-solving strategy.” 

Kim added that students “can’t get to the solution if they can’t get to the start,” emphasizing the importance of learning the fundamentals. Just as mastering the Pythagorean Theorem is necessary to identify problems that can be solved by it, in math and many other subjects the most valuable skill you can develop is the ability to apply the correct tools to solve correct problems. Interleaving develops that skill by forcing the brain to “retrieve” or “dig up” previously learned information.

Instead of always giving students problems involving the most recent concept students have learned, try incorporating a mixture of problem types into student homework, exams, and review sessions. This is particularly helpful for problems that look similar, but require different strategies, or for problems that look quite different, but can be solved with the same strategy.

Author: Ulrich Boser