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I am Mark McDaniel, Professor of Psychology

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and Education at Washington University in St. Louis.

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Spacing is a technique that's alternative to the common practice

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of presenting one particular topic or kind of content in one session.

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Spacing would take the same amount of time that you would spend on one lesson

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and divide that time into smaller chunks, and these smaller chunks would be distributed

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across several days or several weeks rather than presenting the material at once.

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The research shows that spacing produces robust advantages in retention of material

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and sometimes in transfer of material.

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So an example would be an experiment that was done

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in a middle school biology classroom-I'm sorry,

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middle school science classroom-and the lessons involved some biology topics,

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one of which was mitosis.

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The researchers took the mitosis lesson, which generally was presented in one class

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and during the lesson, terms would be repeated and so on,

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and divided the amount of time that was generally spent on that lesson,

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took some portion of the time, and spent it on mitosis after an animal reproduction section.

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Then a little bit more of that time was spent after another lesson-plant reproduction.

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So the same amount of time spent on mitosis but in one case,

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it's presented in one lesson as it typically would be, in another case,

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that information is sectioned off into smaller units of time

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that are distributed among other kinds of topics.

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And it turns out that three weeks after a presentation of these lessons,

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that these middle school kids were 50% better on average at answering questions

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about the particular terms, generating the terms to fill in the blank,

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and I think more impressive, in answering essay questions that ask the kids

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to describe what mitosis is and to illustrate the process.

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So, again, the same amount of time is spent on these terms in this unit,

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but in one case it's spaced over several different lessons, if you will,

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or reviewed-there are little reviews across other lessons-in the other case,

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it's the more traditional method of presenting everything in one session

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and then moving on to other topic.

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I think in education we can distribute and space our instruction much more

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than we are doing now to really tremendous benefits.

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Now, it's going to be a little bit of a challenge for teachers because they are used

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to spending all their time on one topic and one lesson.

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But they don't need to spend anymore time,

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they just have to think a little bit about saving-reserving some time for a particular content

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and bring it back about a week later, two weeks later, and so on throughout the semester,

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and this is going to promote much better retention and learning.

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You can even see the effects in motor learning/skill learning type of situations.

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For example, practicing an instrument-it's better to practice

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in a spaced fashion 30 minutes a day for the week rather

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than two one-and-a-half-hour sessions throughout the week.

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In fact, college baseball teams have used this principle

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to help improve the batting proficiency of their hitters.

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At Cal Poly Tech, a study was done in which hitters practiced hitting 15 fastballs all at once,

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15 curveballs, and 15 change-ups three times a week over a five-week practice session,

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and that was compared to a spaced or distributed practice situation

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where the hitter would hit a fastball, then maybe a curve ball, then maybe a change-up,

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then maybe another change-up, then a curve ball.

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So the practice on 15 of each kind of pitch is spaced over the whole session

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and these hitters were much better-who got the spaced practice-than the hitters

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who got the mass practice.

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So in virtually every kind of content you can think about, spacing the presentation

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or practice of material produces much better retention than massing the practice.

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Now, some teachers are going to ask-it's a good question, too-"Well,

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what are the timeframes in which I should space the material?"

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The optimal spacing, more or less,

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for promoting retention at 30 days is about a review every six days.

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So you can see if you want to retain things for about a year, really, we ought to be spacing

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and reviewing content every couple of months in our classrooms.

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There are some interesting reasons why spacing is going to promote retention.

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Spacing the information now is presented once you have forgotten

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and once the original lesson has left awareness.

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So on the next presentation, you have to retrieve the information,

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you have to get it out of long-term memory, and that, then, creates a more focused,

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a more attentive, a more engaged interaction with the material

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on the second and the third presentations.

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Moreover, these second and third presentations are coming in a different context.

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They are coming in a context in which additional information has been learned,

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and so these spaced presentations allow what we would call "variable encoding"-chances

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to encode the information in different ways, get different perspectives on it,

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understand it a little bit differently, relate it to prior knowledge.

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All of these things are instrumental in learning and good retention.

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Spacing fosters that.

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If our goal in education is for long-term retention of material-that is,

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if our goal is that the kids learn information that they can retrieve and use a year later

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or two years later or three years later-we really ought to be spacing our practice.

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