Interleaving is a learning technique where students mix, or interleave, multiple subjects or topics while they study in order to improve their learning. Unlike blocked practice, where students study one topic thoroughly before moving to another, interleaving involves switching between topics, skills, or problem types.

The Science Behind Interleaving's Effectiveness

1. Discrimination Learning

When students interleave different topics or problem types, they must learn to distinguish between them, identifying the relevant features and appropriate solution strategies for each. This enhances their ability to:

  • Recognize when to apply specific concepts or methods
  • Notice subtle differences between problem types
  • Build stronger mental representations of concepts

2. Retrieval Practice Enhancement

Interleaving naturally incorporates retrieval practice—the act of recalling information from memory—which is known to strengthen learning. When switching between topics:

  • Students must repeatedly retrieve different sets of information
  • The retrieval effort is greater than in blocked practice, leading to stronger memory traces
  • Connections between different topics become strengthened

3. Desirable Difficulty

Interleaving introduces a "desirable difficulty" into the learning process. While this makes studying feel more challenging, cognitive science research shows that:

  • These difficulties lead to deeper processing of information
  • The increased cognitive effort results in more durable learning
  • Students develop more flexible knowledge application skills

Example: Math Problem Solving

Consider studying three types of calculus problems:

  • Blocked practice: Solve 10 derivative problems, then 10 integration problems, then 10 optimization problems
  • Interleaved practice: Solve a mix of derivative, integration, and optimization problems in an unpredictable sequence

With interleaving, students must first identify the problem type before selecting the appropriate strategy. This mimics real-world application and exam scenarios where problems aren't pre-categorized.

Neurological Basis

Interleaving works by engaging multiple neural networks and strengthening the connections between them. Research shows that:

  • Varied practice activates different brain regions associated with different types of learning
  • Spacing different topics allows for memory consolidation processes to occur
  • The context-switching required during interleaving enhances cognitive flexibility

Research Support

Multiple studies demonstrate interleaving's effectiveness:

  • Rohrer and Taylor (2007) found math students who practiced problems in an interleaved manner performed 43% better on a delayed test than those who used blocked practice
  • Kornell and Bjork (2008) showed interleaving improved students' ability to distinguish between artistic styles
  • Birnbaum et al. (2013) demonstrated interleaving's benefits for category learning

Practical Benefits in Learning

  • Transfer of learning: Students develop better ability to apply knowledge to new situations
  • Metacognition: Enhanced awareness of one's own learning processes and strategy selection
  • Long-term retention: Information studied through interleaving tends to be remembered longer
  • Reduced forgetting: Regular revisiting of topics minimizes the forgetting curve

Conclusion

Interleaving works because it better reflects how we naturally encounter and use information in the real world. By practicing discrimination between different concepts, enhancing retrieval strength, and introducing desirable difficulties, interleaving creates stronger, more flexible, and more durable learning than conventional blocked practice methods.

While it may initially feel more difficult and less productive than blocked practice, the cognitive benefits of interleaving make it one of the most effective evidence-based learning strategies available to students.