Interleaving is a process where students mix, or interleave, multiple subjects or topics while they study in order to improve their learning. Blocked practice, on the other hand, involves studying one topic very thoroughly before moving to another topic. Interleaving has been shown to be more effective than blocked practice for developing the skills of categorization and problem solving; interleaving also leads to better long-term retention and improved ability to transfer learned knowledge. This strategy forces the brain to continually retrieve because each practice attempt is different from the last, so rote responses pulled from short-term memory won’t work. Cognitive psychologists believe that interleaving improves the brain’s ability to differentiate, or discriminate, between concepts and strengthens memory associations. Because interleaving involves retrieval practice, it is more difficult than blocked practice. It is important to remember that effortful studying feels worse but produces better long-term results.
Whereas blocking involves practicing one skill at a time before the next (for example, “skill A” before “skill B” and so on, forming the pattern “AAABBBCCC”), in interleaving one mixes, or interleaves, practice on several related skills together (forming for example the pattern “ABCABCABC”). For instance, a pianist alternates practice between scales, chords, and arpeggios, while a tennis player alternates practice between forehands, backhands, and volleys.
Over the past four decades, a small but growing body of research has found that interleaving often outperforms blocking for a variety of subjects, including sports and category learning. Yet there have been almost no studies of the technique in uncontrived, real world settings—until recently. New research in schools finds that interleaving produces dramatic and long-lasting benefits for an essential skill: math. Not only does this finding have the potential to transform how math is taught, it may also change how people learn more generally.
What are some interleaving strategies?
To interleave while studying, students should choose several topics and spread them throughout their study sessions. The topics can be from the same or different subjects, but some experts believe that this strategy is most beneficial when the subjects are related in some way. For example, during a study session, a student could devote some time to math, some time to chemistry, some time to biology and then cycle back through the topics, possibly studying the topics in a different order and using different study strategies. Changing things up forces students to retrieve information and make new connections between the topics: for example, how is this topic in biology related to what was just studied in chemistry? It is important to devote enough time to each topic to ensure that a deeper understanding is achieved each time the topic is studied. Learners should be careful not to use interleaving as an excuse to switch to another subject when the current subject becomes too challenging. Instead, they should persist in one subject until they have a sense of accomplishment before moving on to another subject.
Interleaving boosts learning by mixing up closely related topics, which encourages students to develop the ability to distinguish between multiple concepts. For example, learning increases when students practice addition, subtraction, multiplication and division problems all mixed up, rather than one type of problem at a time.
The Chartered College of Teaching's Impact Magazine has a useful article on interleaving which you can read here