Most students study in blocks — twenty algebra problems in a row, then twenty geometry problems. It feels efficient because performance during the block improves quickly. Interleaving, which mixes problem types together, feels harder and slower in the moment, but produces stronger retention days and weeks later.

The reason is that blocked practice lets students succeed by pattern-matching to the previous problem rather than truly identifying which method a problem calls for. Interleaved practice forces that identification step every single time, which is exactly the skill students need on a real exam where problem types are mixed.

Introducing interleaving gradually — mixing two related topics before attempting a fully mixed review — helps students get past the initial frustration of feeling like they are doing worse, when in fact they are learning more durably.