Interleaving

Interleaving is mixing different types of practice or topics within a session instead of blocking — doing one skill or subject until done, then the next. Blocked practice feels productive: you get into a groove and see quick gains. Interleaving feels harder: you keep switching, retrieval is effortful, and progress feels slower. The counterintuitive result: interleaving produces better long-term retention and transfer. When you block, you're often recognising the pattern and repeating a procedure. When you interleave, you're forced to discriminate: which strategy applies here? That discrimination builds the right kind of learning.

The effect shows up across domains. In motor skills, mixing practice of different shot types (e.g. tennis forehand, backhand, volley in random order) beats blocked practice of each. In maths and science, alternating problem types within a session beats doing all of type A then all of type B. In studying, mixing topics or question types improves exam performance compared to one-topic-at-a-time. The mechanism: blocked practice lets you lean on short-term memory and surface cues. Interleaving forces retrieval from long-term memory and strengthens the link between context and the right move. You learn when to apply what.

Building and scaling depend on transfer — using what you learned in one situation in a new one. Interleaving improves transfer because you're not overfitting to a single context. Teams that rotate through different types of tasks (e.g. alternating bug fixes, features, and refactors) often develop more flexible judgment than teams that specialise in long blocks. The cost is upfront difficulty and the feeling that you're not "finishing" anything. The payoff is durable, generalisable skill. Use it when the goal is retention and transfer, not just session fluency.