Interleaving

What is interleaving?

Interleaving is a learning strategy in which different types of problems, topics, or skills are mixed within a single practice session. It is the opposite of blocked practice (blocking), where one kind of task is practised to completion before the next begins. Instead of the order AAA BBB CCC, interleaving uses a mixed sequence such as ABC BCA CAB.

How does it differ from blocking?

With blocked practice you already know the right strategy, because every problem in a block is the same kind. With interleaving you must decide anew for each problem which method applies. This act of choosing the correct strategy is exactly what is required on a later test or in real-world use.

What does the research show?

In a widely cited study by Taylor and Rohrer (2010), interleaved practice initially lowered performance during practice yet doubled scores on a test given the next day. The authors attribute the benefit mainly to interleaving improving the ability to pair each problem with the appropriate procedure. A later field study by Rohrer, Dedrick, and Stershic (2015) with seventh-graders likewise found substantially higher test scores for interleaved practice, especially on a test taken 30 days later.

How should interleaving be judged?

Interleaving is closely related to the spacing effect, because mixing also distributes repetitions over time. It works best when the mixed items are similar or easily confused – then it specifically trains discrimination. In practice it is easy to apply: deliberately mix exercises from different topics instead of working through them chapter by chapter; this is especially helpful for exam preparation, because exams rarely present neatly sorted problems of one kind either. The evidence is mostly positive but varies in size by subject and design; meta-analyses report small-to-moderate effects for mathematics problems. Because interleaving makes practice more effortful, it often feels less effective in the short term than it is in the long term – an example of a "desirable difficulty."