Concept
Interleaving
Interleaving is a practice method in which different problem types or skills are mixed within a single session, so each question forces you to decide which approach it calls for before you solve it.
Most practice comes in blocks: fifteen problems of one kind, then fifteen of the next, which is how most textbook chapters are laid out. Inside a block, the method is decided before you read the question. You already know it's a ratio problem because the last six were. You get faster and more accurate, and it feels like progress. But on an exam, at work and in real life, problems arrive unlabeled. Interleaving puts that labeling job back into practice. Sessions feel slower and you make more mistakes. That is why learners rate blocked practice as more effective, even though interleaved practice wins on tests taken days later. The gap is a desirable difficulty: the effort of telling methods apart is the learning itself. It works best once you've met each type at least once. Mixing topics you've never studied just adds confusion.
A real-life example
Sam is studying for a statistics final. He works chapter by chapter, first t-tests and then chi-square, and scores around 90% on each chapter quiz. On a mixed mock exam he scores 60%. He can run every test, but he can't tell which one a question needs. He changes his routine: each evening he does 12 problems drawn from all three chapters and writes the test's name before calculating. His scores dip to 70% at first. On the final he hits 85%.
How to use it
- 1Pick three or four problem types you've already met once, shuffle their problems into a single set, and hide the chapter headings.
- 2Before solving each one, write a single line naming the method it needs and why. Check that choice first, then the answer.
- 3Expect lower scores in the first sessions. Judge the method by a mixed test a week later, not by how smooth practice felt.