Interleaved practice: mixing problem types

In short: With interleaved practice you work on different but related types of problems in a mixed order instead of one type after another in blocks. It feels harder, but in many studies it leads to better retention and application.

In more detail: In blocked practice you already know before each problem which method is needed. When problems are mixed, you first have to recognise which method fits, and that is exactly the decision exams require. The effect is best documented in mathematics and in learning to tell categories apart.

In detail

• Blocked practice: First ten problems on the area of triangles, then ten on circles. It feels smooth and successful.
• Interleaved practice: Triangles, circles and trapezia all mixed up, so you have to think afresh each time.
• Why it helps: You learn to distinguish problems and choose the right tool instead of just repeating one procedure mechanically.
• Evidence: Studies by Doug Rohrer on maths teaching and by Nate Kornell and Robert Bjork on recognising painting styles, among others, showed advantages over blocked practice.
• Feelings are misleading: Many learners think blocked practice is more effective because it feels easier; interleaving is one of the so-called desirable difficulties.
• Basics first, then mix: With completely new material it makes sense to understand a method briefly in a block before mixing.
• Only mix related topics: The idea is to mix similar topics within one subject, not to jump randomly between English and chemistry.
• Works well with other methods: Interleaving combines well with self-testing and spaced repetition (testeffekt-und-abrufueben, vergessenskurve-und-wiederholen).