Interleaving is a learning technique where students mix, or interleave, multiple subjects or topics while they study in order to improve their learning. Contrary to the more common method of blocked practice (focusing on a single skill at a time), interleaving involves practicing multiple skills in a mixed sequence.
Cognitive Science Foundations
The effectiveness of interleaving is supported by multiple areas of cognitive science research:
1. Contextual Interference Effect
When learning is made more difficult in the short term, it often leads to better long-term retention and skill transfer. Interleaving creates what researchers call "desirable difficulties" that enhance learning.
Research Highlight: Shea and Morgan (1979) conducted pioneering research showing that participants who practiced tasks in an interleaved manner performed worse during practice but significantly better on delayed retention tests compared to those who practiced in blocks.
2. Discrimination Learning
Interleaving helps learners identify the subtle differences between problem types or concepts. By switching between different types of problems, students become better at distinguishing when to apply specific solution strategies.
Research Highlight: Kornell and Bjork (2008) found that interleaving examples of different artists' paintings led to better later identification of new paintings by those artists compared to studying each artist's works in separate blocks.
3. Retrieval Practice Enhancement
Interleaving forces learners to retrieve information from memory more frequently, which strengthens memory pathways and improves recall.
4. Spacing Effect
Interleaving naturally incorporates spacing (distributed practice over time), which has been consistently shown to improve long-term retention.
Brain Activity During Interleaving
Neuroimaging studies have revealed several important insights about how interleaving affects brain activity:
- Increased prefrontal cortex activity - This brain region is associated with executive functions like decision-making and strategy selection
- Enhanced hippocampal activation - Associated with memory formation and consolidation
- Greater connectivity between brain regions - Suggesting more integrated learning
Interleaving vs. Blocked Practice: The Evidence
| Study Area | Key Findings |
|---|---|
| Mathematics | Rohrer et al. (2015) found that students who practiced math problems in an interleaved fashion scored 63% higher on a delayed test compared to students who practiced in blocks. |
| Motor Skills | Research in sports science shows interleaved practice leads to better retention and transfer of motor skills in baseball batting, basketball shooting, and other physical activities. |
| Category Learning | Studies by Birnbaum et al. (2013) demonstrated that interleaving helps learners better categorize items and develop more robust conceptual understanding. |
| Language Learning | Research suggests interleaving vocabulary words from different categories improves retention compared to studying words from the same category together. |
Why Interleaving Works: The Mechanisms
- Attention enhancement - Switching between topics maintains higher levels of attention and engagement
- Strategy selection practice - Learners must repeatedly choose which strategy to apply, strengthening these decision-making skills
- Reduced forgetting - The time between practice sessions of the same type creates optimal spacing for memory consolidation
- Elaborative processing - Comparing and contrasting different types of problems leads to deeper understanding
- Contextual variation - Learning material in varied contexts promotes more flexible knowledge application
The Challenge of Implementation
Despite strong evidence supporting interleaving, it faces implementation challenges:
Interleaving typically feels more difficult and less productive to learners compared to blocked practice. This creates a "illusion of competence" with blocked practice that can mislead both students and teachers about effective learning strategies.
Students often report lower confidence and satisfaction with interleaved practice, even though their actual learning outcomes are superior. This metacognitive disconnect represents one of the biggest barriers to wider adoption.
Optimal Implementation
Research suggests these best practices for implementing interleaving:
- Introduce concepts through blocked practice before transitioning to interleaved practice
- Interleave related but distinct concepts/skills rather than completely dissimilar ones
- Gradually increase the difficulty and variety of interleaved material
- Combine interleaving with other effective learning strategies like retrieval practice and spaced repetition
The science behind interleaving represents a powerful example of how cognitive psychology research can inform educational practice. By challenging learners to continuously retrieve and apply knowledge in varied contexts, interleaving creates the conditions for more durable and flexible learning, even though it may initially feel more difficult and less productive than conventional study methods.