In schools all over the world, subjects are being taught in the same way: one thing at a time. We first learn one concept of math before moving on to the next. We take history one era at a time. The whole education system is structured around that one-at-a-time concept. We take 45 minutes of one class, then 90 minutes of another, and so on.
Of course, as this is the way we’ve learned since we were children, we naturally pick it up in all our learning from then onwards. We do the same when learning for work, when practicing instruments and sports, and everywhere else. But, an increasing number of studies suggests that this whole concept is wrong. The (better) alternative is studying a few things at a time, a process called interleaving.
What is interleaving?
Interleaving is the process of mixing different topics and skills together while learning. Most often, it is either the mix of actually different topics, like math and chemistry, or the mix of old and new material. In the second case, instead of studying/reviewing things in a chronological order, you mix it up to improve retention of the topic.
The opposite is blocked practice (sometimes called blocking). Blocked practice is when you practice one thing at a time, while ignoring everything else. Most often, the learner tends to practice that particular thing very thoroughly, before moving on to the next item.
Why is interleaving effective?
The first reason why interleaving works so well is that, by mixing up your learning, you make your brain understand the context better. When we spend too much time on the same thing, our brain tends to find the easy way out. It identifies patterns that emerge in the specific set of problems, and recalls these from short-term memory, instead of actually solving the problems. On the other hand, when you utilize interleaving, your brain is forced to apply knowledge to a variety of problems, and thus it builds stronger neural connections.
What may be even more important in the process of interleaving, is the amount of retrieval (recall) necessary. As our brain constantly needs to employ different pieces of knowledge to solve the problems thrown at it, it constantly needs to retrieve stuff from the long-term memory. We’ve talked before about how important recall is in memorization. Therefore, by using interleaving, you immensely improve the long-term retention of the information you learn.
Note that both understanding the context and recall are active learning strategies. That means, that when learning with interleaving, you have to be focused and attentive to the process. To understand more about the benefits of these, and how to actually achieve them, make sure to read my article on deliberate practice.
When is interleaving useful (and when is it not)?
While interleaving can be useful in most scenarios, most experts agree that the skills and concepts interleaved should be at some level related. For instance, if combining different aspects of playing the guitar, it doesn’t make much sense to interleave it with studying English grammar.
A great example of when to use interleaving is sports, for instance, tennis. Instead of just practicing backhands in one session, you can interleave backhands, forehands, and volleys to get increased results. The same thing applies to playing an instrument, like piano, where you could interleave scales, chords, and arpeggios, for instance, instead of practicing only one of those at a time.
Note, though, that interleaving is not constrained to mechanical skills, like sports and music. Another great example can be found in science classes, where interleaving math, physics, and chemistry, for example, can provide you with an advanced understanding in all 3 fields.
In general, interleaving has been proven to be a great strategy for most mechanical skills (sports, music, video games, etc.) and problem-solving based subjects, like math. Also, it has been proven effective on any subjects, as long as the interleaved subjects are of the same category.
A quick insight from a study on interleaving
In a study from 2012, Doug Rohrer from the University of South Florida, Tampa, explored the effect of interleaving on students. His study was one of the first to explore interleaving in real-life education contexts, as most evidence until then was on things like sports and hands-on training. To conduct his study, he worked with 9 classes of 7th graders, on the topics of algebra and geometry.
The study involved teaching the students slope and graph problems. While the lectures remained almost identical, the worksheets that were handed out were different. Five classes received worksheets based on interleaving for slope problems, and based on blocked practice for graph problems. The other four classes received the opposite combination. The interleaved worksheets contained problems of different types mixed together, while the blocked ones had problems of the same type.
Five days after the last lesson, all the students went through a review session. Then, a surprise test was given one day or one month later. The results from the next day showed a 25% better performance for the problems trained with interleaving. The results from the next month, though, showed an amazing 76% advantage for the problems trained with interleaving versus the ones trained with blocked practice.
Source (and suggested for further reading): This great article by scientificamerican.com
Interleaving is best for long-term
Based on the study above, it’s easy to see the amazing long-term effects of interleaving. As our brain has put more effort into learning (which is practically why interleaving works), our long-term retention of the subject is immensely better than it is with blocked practice. That’s also why interleaving works great in combination with spaced repetition, which is the most important technique for long-term retention of knowledge.
It’s important to know this, as one thing that most studies have shown is that interleaving does not have the best immediate results. While the study above showed increased performance the next day, right after the practice session the results may be the opposite. In fact, most learners feel like blocked practice is the easiest and most effective strategy right after the practice session. It is only after the next day comes that interleaving starts showing results.
Interleaving works because it actually challenges us, and, usually, this challenge may be slightly unpleasant during practice. But, it has so profound long-term results that it is absolutely worth it. That shows that what feels more efficient and effective on the spot is not always what’s best for long-term learning and retention.
Avoid common mistakes
The most common mistake people commit when practicing with interleaving is switching tasks too quickly. When you switch quickly, you transform interleaving to multitasking, and multitasking does not work.
When you switch tasks and topics, there is something called ‘task-switching cost’. If you don’t allow yourself some time to diffuse, part of your focus remains (unconsciously) with the previous task. That effect has been calculated to reduce up to 40% of your productivity on the new task. Therefore, you should not only avoid switching tasks too often when interleaving, but when you do so you should take a 5-minute break to allow your brain to get into diffuse mode.
The second common mistake is quitting because it feels challenging. Interleaving is quite unconventional to the way we’ve learned to study, and thus will feel foreign to you when you start using it. That is expected, and you will need to push through until it becomes the natural way to learn.
Some final notes on interleaving
Based on all the things we’ve covered in this article, it’s probably obvious that interleaving does not necessarily make studying and practicing easier. In fact, it probably makes it harder, as it is more challenging for the learner. Nevertheless, it makes learning much more effective in the long-term, and also helps a lot with memorization. That makes the trade-off worth it, as the results are much greater than the change in difficulty.
Finally, interleaving should be used along with all the learning techniques, if you want to reap the maximum benefits. Make sure to read up on processes like spaced repetition, deconstruction, and building stakes, as well as any of the other learning how to learn concepts covered on this blog. This way you will be able to maximize the effectiveness of your learning, while boosting it further with interleaving.
Call to Action
If you liked this article, please share it with your friends. Also, as you start utilizing interleaving in your learning, you are soon going to witness the difference in your comprehension. Let me know about your experience, and share with me any questions you may have. Leave a comment below, or contact me directly at email@example.com!