the theoretical underpinnings of the varied practice approach stem primarily from a behavioral phenomenon discussed in the skill acquisition literature called contextual interference (shea & morgan, 1979). contextual interference refers to a learning benefit observed when the items to be learned are randomly intermixed across training blocks rather than repeated in blocks (for a review, see magill and hall, 1990). that is, when identical items are blocked together during training, post-training performance is worse than when different items are intermixed. although primarily studied with motor skill learning task, contextual interference was originally reported in a verbal paired associates task (battig, 1966, 1972) and has been observed in other non-motor tasks (e.g., carlson et al., 1989). the benefits of mixed-item blocks are apparent only some period of time after practice, indicating that the effects are primarily long-term.