Interleaving vs. blocking: how to order your studying

Most people study "blocked": all the algebra problems, then all the geometry problems, then all the trig problems. It feels organised, and it feels like you're improving fast, because within a block you get better at recognising the pattern for that specific problem type quickly.

The alternative is interleaving: mixing problem types together so you don't know what kind of problem is coming next. Doug Rohrer and Kelli Taylor's classroom studies on this are the ones usually cited - students who practised math problems interleaved outperformed students who practised the same problems blocked, on a test given days later, even though the interleaved group felt like they were doing worse during practice.

Why blocking feels better and works worse

In a blocked set, once you know the category, you can often apply a memorised procedure without deciding anything. That's fast and smooth, and it's exactly the kind of fluency that doesn't transfer - real exams and real problems don't announce their category first. The actual skill you need is knowing which approach to use, and blocked practice never asks you to develop that skill because the category is never in doubt.

Interleaving forces you to identify the problem type before you can even start solving it. That's the harder, slower, more useful task - another case of a desirable difficulty.

Where this applies beyond math

The clearest evidence is in problem-solving subjects (math, physics, statistics), but the underlying idea generalises to any subject where you have to identify something before you can answer about it: distinguishing similar diagnoses, similar historical periods, similar grammatical cases, similar chemical reactions. If two concepts are easy to confuse, studying them side by side - not one after the other in isolation - is what actually trains the distinction.

What to do with this

Don't finish one topic's flashcards before starting the next. Mix decks, or make sure your review queue pulls from several topics at once.
Expect it to feel worse in the moment. You'll be slower and get more wrong early on. That's the signal it's working, not a sign to switch back.
This is one reason a single mixed review queue beats studying one deck start-to-finish - the mixing is doing real work, not just adding variety.