It might seem advantageous when studying to do a large number of practice problems for one topic before moving onto the next topic. On the contrary, studies have shown that it is better to complete practice problems for a variety of topics within each study session. This has been shown to facilitate learning and help students distinguish between different classes of problem. In other words, rather than only completing problems on a newly introduced topic in a study session, instead mix in problems from previous topics. This type of study strategy is known as interleaved or shuffled practice.

Interleaving is particularly relevant for learning a subject like maths. Solving a problem in a test or exam requires students to choose the appropriate technique then execute it. If when studying, the problems are blocked together, then students can miss out on developing the skill of choosing the appropriate technique.

When a new topic / type of problem is introduced, first practice that type of problem. Then in the same study session interleave examples of the new type of problem with others introduced in previous study sessions. The downside of this is that study sessions might take a bit longer, and be more mentally demanding, due to the need to switch between types of problems. Yet this switching engages cognitive processes that help improve learning in the long run. It is the interleaving of new and previous styles of problem which creates a benefit on top of what can be achieved from other study methods [1].

One study by Rohrer and Taylor found that shuffling maths problems concerning the calculation of volume of different shapes was more effective than solving blocks of problems for each shape, even though the total number of problems solved remained the same [2]. Kornell and Bjork compared studying the works of a particular painter blocked together compared to interleaving the works of various painters. In a later test where participants had to identify who painted each of a novel series of paintings those who were in the interleaved group did a better job at matching paintings to artists [3].

It’s worth noting that a study by Hausman & Kornell found that mixing different subjects together didn’t boost learning. Their experiment involved mixing the study of anatomy terms with learning Indonesian [4]. This suggests that interleaving the study of two disparate subjects is a step too far. Instead it is better to limit ourselves to interleaving topics within a subject.

In some scenarios, interleaving may be difficult to incorporate into study practice. If this is the case, don’t stress about it and instead concentrate on other study strategies. One scenario where it is both advantageous and easy to include is vocab learning. Rather than bunch together all vocab items from a single category like food, mix up vocab items from different categories. For those using flashcards, interleaving naturally occurs if students have one large deck for a given course.

Textbooks and problem sheets from a course typically have blocks of problems devoted to the same concept. In some subjects, lecturers have traditionally assigned large sets of problems for homework. Yet there is no evidence that students will benefit from working through large blocks of the same style of practice problem in one session [5]. Instead, do a few of a given type of problem to learn the concept. Then, rather than continuing to trudge through a large number of problems, spend some time doing problems from previous sections.

In conclusion, interleaved practice not only helps learn to solve a particular type of problem but develops the ability to choose the appropriate strategy. This aligns to what will be encountered in an exam or test.