🔀 Learn More by Mixing Things Up

The science of interleaved practice

Learning is part of becoming a better person, but it’s not always easy. We spend most of our school years studying what curricula tell us to learn, and we rarely focus on improving how we learn. The how is fundamental though; if learning is unnecessarily difficult or boring, quitting is only around the corner.

If you’re trying to master a new skill or develop your knowledge, you ideally start by setting the right goals and adopting the best learning techniques. But most of us approach learning without considering the simple rules that maximize progress. I’ll focus here on one particular learning principle that is commonly ignored: Instead of learning in blocks—focusing on one thing at a time—you should mix things up. This is what scientists call “interleaved learning”.

Comic from @sabincomics

🌍 Does interleaved learning work in the real world?

In a recent study, researchers at UCLA tested the efficacy of interleaved learning in a real-world setting. Plenty of lab-based research on this question already exists, but it’s important to examine how it translates to real life.

Universities provide the perfect real-life environment in which to compare different learning strategies because classes contain large numbers of students, high educational stakes, and quantitative grades that track performance. So the researchers went to a major US university and recruited 350 undergraduate physics students.

Like most courses, a physics course contains a varied list of topics for an academic term. Topic titles for this group of students included “Magnetic field”, “Quantum mechanics”, and “Charges, atoms, electric forces”.

Across 8 weeks of study, students received 20 homework assignments. Half of the students received assignments containing interleaved topics, while the other half received assignments containing blocked topics. After 10 assignments, the groups switched so that every student tried both types of learning.

Blocked assignments involved studying each topic separately, which means students only moved on to a new topic after completing all activities for a prior topic. In contrast, interleaved assignments bounced students from one topic to another as soon as they finished a specific activity. Everyone studied the same material, but blocked students completed entire topics within single assignments, while interleaved students combined diverse but incomplete topics in each assignment. Interleaved learning therefore required several assignments to complete any topic in full.

Here’s an example chart showing how blocked vs interleaved learning might look. If you need to study topics A, B, and C and each contains three parts, you could cover all parts in a single assignment or split the parts across multiple assignments:

The blocked system feels more organized and well-structured, which is probably why most educational programs default to it. But that doesn’t necessarily mean it provides a better learning experience.

Students in the experiment took two surprise tests during the 8-week program to assess how much they had learned and retained from their classes and homework assignments. The surprise element meant they couldn’t use any additional revision or cramming strategies right before the exam. Their performance entirely reflected what they naturally picked up during their regular studies and homework.

So how did the blocked vs interleaved groups compare? Students found the interleaved learning more difficult than the blocked learning and believed they learned less from it. The constant flipping between topics was demanding because it challenged students to switch between different styles of problem-solving within a single assignment.

Despite this, the interleaved students far outperformed the blocked students during the surprise tests. In the first test, their median scores were 50% higher. In the final test, which allowed students to make use of everything they learned across the full 8 weeks, their median scores were 125% higher.

So interleaved learning is better than blocked learning in real-world settings like university education. When you add space between study sessions for any single topic, it forces you to retrieve information from memory as you learn it. When you study a topic all at once, there isn’t much retrieval going on because everything is “online” at the front of your mind. On the other hand, when you study part of a topic on one day, and then another part a few days later, you need to recall the things you learned in the first lesson to help with learning the second. That recall practice strengthens the information in your long-term memory.

Interleaved learning also helps you find connections and relationships between different topics. When you look at topics in an isolated way, you may miss important points of overlap between them. The same efficient problem-solving strategy could work for two very different topics, but you might only notice it if you experience the two topics together.

There may be many other advantages to interleaved learning too. In any case, there’s a clear practical benefit to mixing different study topics together rather than trying to learn them separately. It’s likely that many of the things that make interleaved learning difficult are the same things that make it worthwhile. So don’t shy away from the challenge.

⭐️ Takeaway tips

• Practice interleaved learning: Whether you’re learning to play a musical instrument, trying to pick up a new language, or training new skills at work, practice different components in conjunction rather than isolation. Training plans often separate skills into distinct study sections but that’s not always optimal. Progression is certainly important so you shouldn’t dive into the most difficult parts of a course first. But you can consider whether there are multiple skill types that match your current level of expertise and whether you’d gain more from learning them in an interleaved rather than blocked fashion.

• Embrace challenges: Sometimes, the things that seem most intimidating are also the things that we most benefit from. As the study above shows, interleaved learning is no exception. Make tough challenges manageable rather than letting them scare you off. For interleaved learning, it helps to write down a plan of which topics and skills you’ll practice at each step during your journey. Although interleaved schedules look confusing and messy, they’re perfectly manageable when you commit to a preplanned system on paper.

• Use objective progress metrics: The research students above thought that blocked learning was superior to interleaved learning, but their objective test scores showed the opposite pattern. This is a good example of how flawed our perceptions can be. Whenever you want to learn or practice new skills, find ways to objectively measure your progress so you can see how far you’ve come over time. It’s easy to lose track of this and give up on learning just because it feels like you’re not making progress. Clearly visualizing your gains over time provides an ongoing dose of motivation and allows you to see what is and isn’t working for you.

💡 A final quote

“Progress is only possible by passing from a state of undifferentiated wholeness to differentiation of parts.”

~ Ludwig von Bertalanffy

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👋 Until next time,

Erman Misirlisoy, PhD

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