#15 The One About ... Spacing and Interleaving

why this study

How much impact does the order or type of questions that students answer have on how well they learn the material, and then their ability to remember the answers later?

Is spacing, which is doing little and often, better than cramming? Does interleaving, which is mixing up the type of problems, help more than blocking?

Researchers Doug Rohrer and Kelli Taylor from the University Florida investigated these types of questions by running two studies that were published in the journal Instructional Science. In their first study, they explored the difference between spacing out maths revision sessions over the course of a week compared to cramming them all in one sitting. In the second study, they also measured the impact of working on the same sort of maths problems for the whole session (i.e. blocking) against mixing up the type of questions the students had to answer (i.e. interleaving).

the main findings

#1 In the final test, students who spaced out their revision sessions got an average mark of 74%, whereas those who crammed their revision got 49%.

#2 In the mock test immediately after the revision session, block learning was better than interleaving. However, in the final test one week later, students who interleaved the type of questions they answered got on average of 63% whilst those that had answered the same sort of problem (i.e. blocking) got on average 20%.

related research

There is a wealth of research that highlights the benefits of spacing over massed cramming. Essentially, doing one hour a day for seven days is better than doing seven hours in one day. Other studies have found that using spacing instead of cramming resulted in 10-30% difference in final test results.

The benefit of spacing has been attributed to the advantage that it allows time to forget and re-learn. This process cements that knowledge and helps transfer it into your long-term memory. Research is unclear on what is the exact ideal amount of time, with one study finding that the longer you want to retain information for, the longer the gap between study sessions should be.

There is also a growing body of evidence that has found that interleaving subjects or the types of problems within a subject helps improve long term retention, recall and performance. This is due to the fact that this process gives students opportunity to practice a range of strategies but also the chance to get better at identifying which strategy is most appropriate and likely to succeed. One such study explored the results of having children throw differently weighted beanbags at a target. The children performed better in the final test if their practice attempts had mixed up the order of the weights, as opposed to practicing them in ascending weight order.

classroom implications

Clearly, the type of practice questions and how well spaced out they are affects how much students learn and remember. It is interesting to consider how most maths text books describe a problem (i.e. how to add fractions), and then give ten practice questions on that problem. The authors of the study note that “an increase in the number of massed practice problems did not reliably affect test scores, large gains in test performance were achieved by the use of spacing or mixing, even though neither of these strategies required additional practice problems”. This suggests that teachers can help students improve their learning without increasing the amount of time spent per topic.

Indeed, they also note another benefit of spacing and interleaving as “when practice problems relating to a given topic are spaced across multiple practice sets, a student who fails to understand a lesson (or fails to attend a lesson) will still be able to solve most of the problems within the following practice set, whereas a massed practice set ensures that this student will have little or no success”. Interleaving may take a bit more time than blocking. The students in the study did better on their mock tests straight after their study session, however, they did not learn it as deeply. This suggests that for long term retention, interleaving is far better.