We all know the saying “Practice makes perfect.” According to Malcolm Gladwell’s Outliers, at least 10,000 hours is required to be a true expert. Many of us assume that aspiring experts must cram those hours into uninterrupted practice sessions and master one topic at a time before moving on. But the conventional wisdom of “blocking” – practicing a single skill for an extended period of time – is being challenged by the concept of interleaving. Research suggests practicing several related skills within a single practice session and engaging in repeated but interspersed sessions expedites learning.
I think back to college. There were courses I admit I put off most of my effort until a day or two before the test. I would then “cram” all the information in as quickly as possible. It worked on test day, but if asked the same questions a few months later, I likely would not have known the answers. Had I spread out my learning over the whole semester, doing a little bit of learning and coming back to it, my ability to retain the information would have been much higher.
Imagine filling a bucket with a hose on full force. Let go, and the bucket has water, but it still has lots of room at the top. Try again. Water flies out of the bucket and still there is room at the top for more water when you are done. Now put the bucket under a faucet with a slow drip. Eventually the bucket will not only fill to the top, its water will actually bead up over the bucket’s edge, yet all the water is still retained. It appears learning works much the same way.
During my years of practicing Jiu Jitsu, we successfully used the interleaving method. Instead of teaching students a single technique until they perfected it, we would introduce a technique and not come back to it for a while. We would vary their training exercises. Mastery still required students to exert sustained effort over time but avoiding repetitive practice sessions sped their progress.
Not only do mixed practice sessions increase learning rates, they also improve retention. Upon completion of three months of math instruction, a University of South Florida study showed that middle schoolers taught using the interleaving method tested 25% better than their blocking-educated peers. More impressive, they scored 76% better one month later.
One explanation for interleaving’s dramatic results is that the technique actually makes it difficult for the brain to rely on rote responses. Since practice sessions cover multiple skills, the same approach cannot be applied to every task. Think about your daily commute. Most of us take the same route every day, driving almost on auto-pilot. But what happens if there’s a detour and you find yourself on unfamiliar streets? You’re forced to pay more attention to get where you’re going. Interleaving is taking “deliberate detours” to hone one’s abilities and cultivate critical thinking.
Sleep is another theory for why interleaving works. During sleep, your body moves memories, thoughts, and learning from short term to long term memory. But not all of this information goes from short to long term in one night. Each time you come back to a subject, more of that knowledge is transferred into your long term memory while you sleep, allowing your body to add more pieces to the puzzle and making the learning more permanent.
When training new hires, many organizations teach and test on one procedure at a time over the course of long, consecutive days. This can produce a false sense of mastery, with employees using a single strategy, held temporarily in their short term memories, to fulfill onboarding requirements. For greater, long term impact, training topics need to be varied and sessions need to be conducted in smaller time increments. Topics need to be repeated over time. While it requires more initial effort, the rewards of interleaving make it well worth the extra planning.