Interleaving and spacing are different choices

Interleaving alternates different kinds of examples or problems; spacing distributes practice over time. Interleaving may prompt useful comparisons when learners need to distinguish categories or select a method. Do not assume the same benefit for simple memorization or tasks where the rule is already clear.

Build a short mixed set around the objective

Suppose students need to distinguish Pythagorean-theorem problems from area problems. After introducing each type, mix a few examples and ask students to name which relationship they will use before solving. Then ask them to explain the choice and check the conditions. If accuracy falls sharply because the rule itself is not yet clear, practice one type at a time briefly and mix them again later. This is an illustrative lesson, not a tested classroom result.

Keep the evidence and its limits together

Rohrer, Dedrick, and Stershic (2015) tested interleaved assignments in a specific U.S. middle-school mathematics unit. Firth et al. (2021) systematically reviewed concept-learning studies and discussed boundary conditions such as task type, rule availability, and how distinguishable examples are. These findings do not establish a neural mechanism or universal benefit for every skill and long-term memory task.

Review questions

Does the learner need to distinguish problem types or choose a strategy? Did actual work show better selection after mixing? If the mix creates confusion unrelated to the goal, adjust the sequence.

Sources: Firth et al. (2021), A Systematic Review of Interleaving as a Concept Learning Strategy · Rohrer, Dedrick & Stershic (2015), Interleaved Practice Improves Mathematics Learning