Interleaved practice in physics benefits from collaboration

Background: Interleaved practice is a desirable difficulty that has been suggested to promote deeper conceptual understanding. However, its effectiveness appears to diminish when learning material becomes too complex, likely due to increased cognitive load. Aims: This study investigates whether collaborative learning can enhance the effectiveness of interleaved practice when students engage with complex physics content. Sample: A total of 376 upper secondary students (Grade 12/13) participated in the study. Methods: A 2 × 2 between-subjects field experiment was conducted with four conditions (interleaved vs. blocked practice × collaborative vs. individual learning). The learning content focused on the motion of charged particles in electric and magnetic fields. Learning success was assessed through knowledge tests administered immediately after practice and after an 8-week delay. Results: A significant practice type × social format interaction emerged. The interleaved–collaboration condition yielded the highest learning gains, both immediately and after 8 weeks. Collaboration showed no overall main effect, and interleaving showed no main effect on immediate gains and a negative main effect on delayed gains. Conclusions: The findings suggest that collaboration mitigates the cognitive demands of interleaved practice, enabling its benefits to unfold even in complex learning contexts. The results highlight that desirable difficulties are not universally effective but require appropriate instructional support. Combining interleaved practice with collaborative learning emerges as a powerful strategy to foster lasting conceptual understanding in science education.