Why Blocked Practice Feels Good But Works Poorly
Most people practice in blocks: they drill one math problem type for 20 minutes, then move to the next, or hit the same tennis serve fifty times before switching to backhands. Blocked practice feels productive because performance improves visibly within the session. But a well-known 2007 study by Rohrer and Taylor found that students who practiced four types of geometry problems in mixed, unpredictable order scored more than twice as high on a test a week later than students who blocked their practice by problem type, even though the blocked group appeared to perform better during the practice session itself.
What Interleaving Actually Is
Interleaving means deliberately mixing multiple related skills or problem types within a single practice session instead of mastering one before moving to the next. A musician interleaves by practicing scales, a difficult passage, and sight-reading in short rotating chunks rather than one at a time. A language learner interleaves by mixing vocabulary review, grammar drills, and listening practice in the same session instead of dedicating a full day to each. The mixing forces your brain to actively retrieve which strategy or skill applies to each new problem, rather than passively repeating the same motion or method on autopilot.
Why the Struggle Is the Point
Interleaving feels harder and slower in the moment, and that difficulty is exactly why it works. Cognitive scientists call this a “desirable difficulty”: the extra mental effort of discriminating between similar skills and retrieving the right approach each time builds stronger, more flexible memory traces than the smooth repetition of blocked practice. This is also why interleaving is especially powerful for skills that are easily confused with each other, like similar chord shapes in guitar, closely related grammar rules, or overlapping business frameworks, since blocked practice never forces you to tell them apart.
How to Build It Into Your Routine
Start small: instead of one 60-minute session on a single skill, split your practice time into three or four 15-minute rotating blocks covering related but distinct sub-skills, and vary the order each session so you can’t predict what’s coming next. Keep a simple log of which sub-skills you rotated through, since interleaving only pays off with consistency over weeks, not a single session. It’s uncomfortable at first, and your progress will feel slower in the short term, but if you’re preparing for something you need to actually retain and apply later, like an exam, a sport, or a professional skill, interleaved practice is one of the most well-supported techniques in the learning science literature for making that happen.
