Have you ever heard of interleaved practice? If you had asked me the same question a week ago I wouldn’t have known what you were talking about. In fact I was stumped when my Dad asked me what it was and since I thought he said “interweaved” I struggled to find an answer on Google.
It wasn’t until later in the week that a blog post showed up in my RSS feed with a reference to interleaved practice that I was able to get the correct spelling and search for a definition. Down the rabbit hole I went and I have spent every spare minute since researching.
Interleaved practice was first discovered 30 years ago and has been described as varied practice, variable practice, and mixed practice. It is a proven technique to increase your ability to learn and retain all kinds of knowledge and skills and I am amazed that it is not more popular. If you are serious about learning in the most efficient manner than this technique should definitely be in your toolbox.
What is Interleaved Practice?
How would you go about learning a new skill, memorizing some vocabulary, or learning how to solve a math problem? Most people would review the basics, complete related practice exercises, reach an acceptable level of proficiency, and then move on to the next topic. This is called block practicing.
Block practicing is when you focus on learning one skill at a time. You practice a skill repetitively for a period of time and then you move onto another skill and repeat the process. Interleaving practice on the other hand involves working on multiple skills in parallel.
If you want to learn skills A, B and C then a block practice session would look something like this AAABBBCCC and an interleaved practice session would look like this ABCABCABC (in series) or ACBABCBAC (randomized). The only constraint is that you can’t work on the same type of problem back to back.
How Effective is Interleaved Practice?
Numerous studies have been done to study the effects of interleaving vs block practice. One of the most recent studies involved teaching college students how to calculate the volumes of four obscure geometric solids: wedge, spheroid, spherical cone and half cone.
Students were split into two groups, the Mixers (interleaved practice) and the Blockers (block practice). The Mixers were given all four tutorials and then completed 16 practice problems that were mixed so that each set of 4 problems (1-4, 5-9, etc) included one of each type of problem. The Blockers were given one tutorial and then 4 related practice problems (e.g. Spheroid tutorial and spheroid practice problems) before moving on to the next three types in a similar manner.
Both groups completed two practice sessions and a test each spaced one week apart. The results confirmed the findings of previous studies. The Blockers performed ~29% better than the Mixers on the practice sessions but the Mixers performed 43% better than the Blockers on the test.
Let me repeat that because it is completely counterintuitive. Students using interleaved practice performed worse than their counterparts using block practice during the practice session but performed better when tested at a later date.
How does Interleaved Practice Work?
The exact cognitive mechanism by which interleaving works is not known for sure but there are a couple working theories:
Breaking in a Path (aka retrieval-practice hypothesis)
In order to practice a skill the brain needs to access the knowledge it has and bring it into working memory. With block practice this occurs when the first practice problem is started and does not happen again while the remaining problems are worked. With interleaving practice the brain needs to bring the appropriate knowledge into working memory for every practice problem. This may cause the pathways for those memories to strengthen and allow for better retention.
Imagine walking across a lawn. Every time you walk back and forth across the lawn your path becomes more broken in and visible. Block practice is like walking back and forth only once while interleaved practice involves walking back and forth many times. The more times you walk the same path the better chance you will be able to find it again in a couple days, weeks or months.
Stop and Go Traffic (aka discriminative-contrast hypothesis)
Another theory is that working on similar skills simultaneously forces the brain to differentiate between the two skills. When you only practice one skill over and over the brain knows what it is coming next and doesn’t have to work as hard. With interleaving the brain is forced to figure out what skill each practice problem calls for. This forces the brain to focus more intensely and this may lead to better retention.
Imagine driving down a highway. Block practice is the equivalent of setting the cruise control and zoning out while interleaved practice is more like stop and go traffic. When you set the cruise control it is possible to disassociate from driving and end up at a destination with no memory of the drive while stop and go traffic keeps us engaged an on edge. It is impossible to zone out because we have to keep adjusting our driving style to the current conditions.
These mechanisms are not mutually exclusive and there may be others at play that have not been discovered yet.
Tips For Using Interleaved Practice
Studies have shown the positive effects of interleaved practice in a variety of domains including: learning simple motor skills, differentiating painter’s styles, learning badminton serves, interpreting electrocardiograms and identifying birds.
The diversity of knowledge and skills that have been studied and the strength of the effect that has been seen makes me optimistic that this technique can be utilized to learn almost anything if applied correctly.
There is no clear guidance on how to incorporate interleaved practice in your current practice or study routine but based on the research I think it is important to keep a couple things in mind:
- Study the material – Before you can begin practicing you need to seek out instruction on what you are trying to learn. You cannot practice effectively if you do not know how to solve the problem or perform the skill.
- Practice deliberately – This is a supplement to deliberate practice, not a replacement. Whenever you are practicing you should be practicing the tenets of deliberate practice.
- Avoid flow – Block practice allows you to get in a groove which gives a false impression that you know the material. You need to actively avoid that sensation and shift to a different exercise once you feel it occurring.
- Mix in old material – It is important that you mix up your practice material. This can be accomplished by cycling in practice exercises you have already completed. This also has the advantage of leveraging the spacing effect.
- Track your progress - This technique has the potential to frustrate and discourage even the most persistent student. By keeping track of your progress you will have confirmation that you are making progress even though it may feel like you are constantly struggling.
Final Thoughts on Interleaved Practice
The more I learn about interleaved practice the more I wonder how it has remained so obscure in spite of its proven effectiveness. One thought that comes to mind is that it might just be too hard to implement.
Learning is a challenging process that places a strain on your brain and your will. The small wins of making quick progress or getting into the groove can provide the fuel to keep going. It turns out that those feelings may only be illusions of progress and that we may be better off stopping short of those accomplishments and shifting to a different learning curve.
But if we are constantly jumping to the next challenge when do we get a chance to enjoy the fruits of our efforts?
If you enjoyed this post you might also enjoy:
Spaced Repetition: How to Learn Anything and Never Forget It
Pushing Through a Learning Plateau
How to Cram for a Math or Engineering Exam in 24 Hours