Interleaving

Interleaving means mixing different topics or problem types within a single practice session, instead of fully working through one topic in its own block first. The opposite, blocked practice, meaning ten problems on topic A, then ten on topic B, feels easier while practicing, because the same strategy keeps working throughout a block. That's also exactly its weak point.

#A concrete example

In training for evaluating loan applications, one group first practices ten cases on "checking creditworthiness," then ten cases on "assessing collateral," then ten cases on "evaluating payment history," each as its own block. A second group works through the same 30 cases in random, mixed order. During the actual training session, the blocked group performs better, because within each block it already knows what kind of case is coming. In a later test with new, unsorted cases, the group that practiced with mixed order reliably performs better, because it additionally learned which case needs which kind of evaluation in the first place, not just how to carry it out.

#Why interleaving still feels harder

With blocked practice, only one question needs answering: how do I solve this particular type of problem. With interleaving, a second, often underestimated question is added: what type of problem is this in the first place. That extra act of discrimination is exactly why interleaving helps in real work, where situations rarely show up neatly sorted by category.