Most people study one thing at a time by instinct: ten practice problems on the same type of equation in a row, then move to the next type once the first one feels solid. It's called blocked practice, and it feels efficient because you get visibly better within the block. The problem is that feeling doesn't transfer well to a test where problem types are mixed, which is exactly what most real exams and real-world situations look like.
What interleaving actually is
Interleaving means mixing different but related topics or problem types within a single study session instead of grouping them into blocks. Instead of ten problems on topic A followed by ten on topic B, you work through A, B, C, A, C, B in a scrambled order. It feels considerably harder in the moment, and that's not a flaw in the method, it's the entire mechanism behind why it works.
Why the harder version teaches more
Blocked practice lets you settle into a single strategy and repeat it without having to identify which strategy the problem calls for, since you already know from the block you're in. Interleaved practice removes that shortcut. Every problem forces you to first figure out what type of problem it is and which approach applies, before you can even start solving it. That extra step, discriminating between problem types, is a skill on its own, and it's exactly the skill a real exam or a real situation actually demands, since nothing in the real world announces which method to use in advance.
- Blocked practice: repeat the same strategy on similar problems. Feels smooth, builds shallow, context-dependent skill.
- Interleaved practice: switch between problem types in a mixed order. Feels effortful, builds the ability to identify which approach fits which problem.
- The research pattern shows up consistently across math, categorization tasks, and motor skills: interleaved practice looks worse during the session and performs better on delayed tests.
Why it feels worse even though it works better
This is the part that makes interleaving hard to adopt on your own: it produces more errors and feels less fluent while you're doing it, which most people read as a sign they're studying badly. It's the opposite signal. The extra difficulty of constantly re-identifying what you're dealing with is exactly what builds a flexible skill instead of a narrow one that only works when you already know which strategy to use.
Building an interleaved study session by hand is genuinely tedious, since it means deliberately scrambling material instead of working through it in the order a textbook presents it. This is one of the things TopicLearn handles automatically: instead of grinding through one concept in an isolated block, related material gets mixed into review sessions over time, so the practice you get looks more like the mixed conditions of a real exam or a real task, not the artificially clean order of a table of contents.