CONCEPT
Interleaving Effect
The finding that mixing different types of problems during practice produces superior long-term retention and transfer compared to practicing one type at a time—because interleaving forces discrimination between problem types, the foundation of judgment.
Interleaving—presenting problems or skills in mixed rather than blocked sequence—makes practice feel less successful (learners are slower, make more errors, report lower confidence) while producing dramatically better performance on delayed tests and transfer tasks. The canonical demonstration: students practicing volume calculations for four geometric solids in interleaved order performed three times better on a delayed test than students who practiced each solid's problems in a separate block, despite performing worse during practice. The mechanism Bjork identified: interleaving forces the learner to examine each problem's features and determine which solution strategy applies before executing it. Blocked practice eliminates this discrimination step—the problem type is predetermined by the block—allowing fluent execution without the categorization work that professional judgment requires.
In The You On AI Field Guide
The interleaving effect illuminates the architecture of professional expertise more clearly than perhaps any other finding in Bjork's framework. Experts do not merely possess more solutions than novices; they perceive problems differently, seeing structure and category where