A closer look at Spacing and Interleaving

Research into both student learning and cognitive science tells us that learning requires repetition. This seems intuitive. But how should repetitions be scheduled? When learning a new concept, should students study that concept again immediately? Or should they wait a while and study it again later? A related question is how to schedule repetitions of similar concepts within a subject. When students learn about fractions, for example, should they practice one type of fractions problem over and over (e.g., how to add fractions) before moving on to a different type of problem (e.g., how to multiply fractions)? Or, would they learn the information better by practicing both types of problems together?


Considering The Spacing Effect first, which is the learning advantage for information that is repeated in a ‘spaced’ fashion. When researchers look at this, they typically put a spacing gap between the first and second studying of some material and then a test delay for the period of time until a test. If the spacing gap is set to zero, then the exposures are said to be massed. Literature reviews of studies (Cepeda, Pashler, Vul, Wixted, Rohler, 2006) showed that regardless of the value of the spacing gap, spaced repetitions typically give better learning than masses repetitions. They also found that longer spacing gaps produced better learning than shorter spacing gaps- sometimes referred to as the lag effect. A recent(ish) study (Cepeda et al, 2008) gave insight into the optimal spacing gap, finding this to be dependent on the test delay- shorter gap spacing gave better retention after short delays and longer spacing gave better retention after longer delays. They found that the spacing gap should be 10- 20% of the test delay.


Simple SPACED example from maths- at the start of a lesson, students are required to review a range of material covered previously in the form of a short test.

Considering next The Interleaving Effect. This means repetitions of different types of material within a particular subject. Again, intuitively it would seem that studying the same type of material over and over before moving on would be best. This approach would be called blocking- a alternative is to mix together the different problem types, which is interleaving. Studies (Rohrer and Taylor, 2007) typically find that interleaving produces better learning than blocking. it has been proposed that interleaving benefits students ability to make important discrimination’s between concepts that are easily confused. It may allow students the opportunity to notice key differences between two similar concepts, helping to make the distinction clear. It has also been noted that interleaving depends on the degree to which the learning task actually requires the noticing of similarities within or between a category. Some research also shows that blocking is more effective when the learning is complex- in such situations, a hybrid approach of initial blocking followed by interleaving.

Interleaved maths

It’s not rocket science, this simple interleaving example in maths requires students to tackle different problem types within the same topic. Most textbooks/ worksheets will group similar types together.

In terms of implementing these ideas into curriculum, we can say that students long- term retention of information is enhanced by reviewing previously learned material. So brief and periodic reviews will help as will including different types of (potentially confusing) problems to leverage from interleaving which strengthen the chances to notice key differences. Cumulative quizzes could also help as a review; both recent and distantly learned. Interleaving also tells us that re-arranging the order of practice problems also helps retention greatly. An obstacle here could be the perception that this is more difficult as students will typically make more errors and move more slowly in comparison to blocking. As forgetting occurs, periodic reviews will help strengthen memory by building on this ‘dormant’ knowledge.


Maths curriculum showing usual blocked approach to the top with an alternative Spaced approach below



Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132, 354-380. DOI: 10.1037/0033-2909.132.3.354.

Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. Psychological Science, 19, 1095-1102. DOI : 10.1111/j.1467-9280.2008.02209.x.

Rohrer, D., & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35, 481-498. DOI: 10.1007/s11251-007-9015-8.


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