Interleaved practice in physics benefits from collaboration

Background: Interleaved practice is considered a desirable difficulty that fosters 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 instructional 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: The combination of interleaved practice and collaboration led to the highest learning gains, both immediately and after 8 weeks. There was no overall benefit of collaboration. Interleaving showed no main effect on immediate learning success and even a negative main effect on delayed learning success.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.