Mixing problem types within a practice session produces worse practice performance and better later retention than practising one type at a time.
Blocked practice lets the learner apply a method without having to select it, which is the part the test will require. Interleaving forces selection every time. The effect is consistent enough to be a teaching recommendation and unpopular enough that few adopt it, because it looks like failure while it is happening.
In practice
- A maths class that mixes topics scores worse on the Friday quiz and better on the summer paper.
- A trainee drilled on one fault type diagnoses it perfectly and cannot tell which fault they are looking at.