The first signs of interleaving’s promise appeared in the domain of motor skills. One early study, published in 1986, involved training students to learn three types of badminton serves. Compared with blocking, interleaving produced better recall of each serve type and better ability to handle new situations, such as serving from the opposite side of the court. Similar results were later reported for baseball, basketball, and other sports. In 2003, one of the first studies to examine interleaving outside of sports found that using it to train medical students produced more accurate electrocardiogram diagnoses than blocking. In 2008, another widely-cited study found a similar benefit for teaching college students to recognize the painting styles of landscape artists. Even critical thinking skills benefit: in a 2011 study, students trained with the technique made more accurate assessments of complex legal scenarios.
Foreign language studies however suggest that the effectiveness of interleaving comes with an important caveat. When native English speakers used the technique to learn an entirely unfamiliar language, such as to generate English-to-Swahili translations, the results were better, the same, or worse than after blocking. These mixed results imply that learners should have some familiarity with subject materials before interleaving begins (or, the materials should be quickly or easily understood). Otherwise, as appears to be the case for foreign languages, interleaving can sometimes be more confusing than helpful.
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Rohrer and his team are the first to implement interleaving in actual classrooms. The location: middle schools in Tampa, Florida. The target skills: algebra and geometry.
The three-month study involved teaching 7th graders slope and graph problems. Weekly lessons, given by teachers, were largely unchanged from standard practice. Weekly homework worksheets, however, featured an interleaved or blocked design. When interleaved, both old and new problems of different types were mixed together. Of the nine participating classes, five used interleaving for slope problems and blocking for graph problems; the reverse occurred in the remaining four. Five days after the last lesson, each class held a review session for all students. A surprise final test occurred one day or one month later. The result? When the test was one day later, scores were 25 percent better for problems trained with interleaving; at one month later, the interleaving advantage grew to 76 percent.
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Researchers are now working to understand why interleaving yields such impressive results. One prominent explanation is that it improves the brain’s ability to tell apart, or discriminate, between concepts. With blocking, once you know what solution to use, or movement to execute, the hard part is over. With interleaving, each practice attempt is different from the last, so rote responses don’t work. Instead, your brain must continuously focus on searching for different solutions. That process can improve your ability to learn critical features of skills and concepts, which then better enables you to select and execute the correct response.
A second explanation is that interleaving strengthens memory associations. With blocking, a single strategy, temporarily held in short-term memory, is sufficient. That’s not the case with interleaving — the correct solution changes from one practice attempt to the next. As a result, your brain is continually engaged at retrieving different responses and bringing them into short-term memory. Repeating that process can reinforce neural connections between different tasks and correct responses, which enhances learning.
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Despite these relative advantages, interleaving remains mostly unknown and unused. Consider the example of grade school math. Out of all the math textbooks used in the U.S. today, all but one type — the Saxon series — uses blocked practice.
We use Saxon math & from what I’ve seen so far, it is awesome.
Random bit of speculation — interleaving isn’t used too much in schools because the classroom format makes it very demanding on the teacher. If you’ve got 30 kids in a room, you have to expect some fraction is not going to ‘get’ any particular topic that comes up. If you are trying to juggle three at once… well, you’d prefer the smallest fraction be completely lost on the fewesr number of topics at a time.
As was explained to me once, the more people you have in a room, the lower the overall IQ gets. The more people you are dealing with, the simpler you’ve got to make things. Blocking is simpler than interleaving.
Interleaving is probably best for self-directed or one-on-one study.
Saxon Math:
I noted that my son was really being shortchanged in HS when he was taking geometry and I examined the textbook he was using. It was abysmal. I had read an article in the National Review some years before about Saxon Math and looked the series up. What I did was that I purchased the 3 Algebra Saxon books, the Advanced Math book and the Calculus book.
I bribed the boy to do the circa 30 problems each day to work through each book in turn with one day off each week, sometimes more on occasion but then he would make up the pace so he was doing six problem sets per week on average. I almost never had to help him and he self taught himself. (BTW, I had a heavy math background during my education.) My son finished the series by the time he was halfway through this senior year in HS.
Did it help him? I would say yes as he is now a Ph.D. Mechanical Engineer.
Dan Kurt
p.s. I didn’t know the term for the Saxon method of reintroducing problems already covered in problem sets was called interleaving. I had called it recursive problem presentation to reinforce math skills. I considered it a brilliant technique.
IOW, replicating the natural pattern of playtime: Do X, get bored. Do Y, get bored. Return to X, Try Z, etc.