Short answer: doing a whole page of one problem type feels efficient and teaches you less than mixing types. Blocked practice lets you skip the hardest step, working out which method the question needs, because the chapter heading already told you.
The evidence
The classic experiment was run on maths problems. Students who practised problem types in a shuffled order performed substantially better on a later test than students who practised the same problems in blocks, even though the blocked group felt more confident while studying (Rohrer & Taylor, 2007). A large meta-analysis has since confirmed the effect holds broadly, with the biggest gains when the categories being mixed are easily confused with each other (Brunmair & Richter, 2019).
That last detail matters for HSFY, because "easily confused with each other" describes most of what you are examined on.
Why it feels worse
Because it is harder in the moment. Blocked practice gets smoother as you go, which reads as competence. Interleaved practice stays effortful, and you make more mistakes while doing it. Students consistently rate the method that works less well as the one they prefer, which is precisely why so few people do this.
What it looks like in each paper
- CHEM191: a set that jumps between a Ka calculation, a Gibbs energy question and an equilibrium-position problem, so you practise telling them apart rather than grinding one.
- PHSI191: alternate a kinematics problem, a fluids problem and a lens problem instead of finishing one module at a time.
- CELS191: mix a dihybrid cross, a recombination-frequency question and a Hardy-Weinberg calculation. These blur together badly under exam pressure.
- STAT115: the most valuable version. Mix scenarios so you have to decide which test applies before computing anything, since that decision is where most marks are won.
How to actually do it
- Learn a topic in a block first. Interleaving is for practice and consolidation, not first exposure.
- Once you have covered two or three topics, stop practising them separately.
- Build mixed sets that do not tell you the topic in advance.
- When you get one wrong, check whether you failed to solve it or failed to identify it. Those are different problems with different fixes.
The payoff
Exams are interleaved by design. Nothing in a HSFY paper announces which lecture a question came from. If all your practice was blocked, the exam is the first time you have ever had to identify a question cold, which is a terrible time to learn that skill.
Cutline sets mix question types by default. Try a mixed set free.
References
- Rohrer, D., & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35(6), 481–498.
- Brunmair, M., & Richter, T. (2019). Similarity matters: a meta-analysis of interleaved learning and its moderators. Psychological Bulletin, 145(11), 1029–1052.
