A number of theories may explain the benefit of spaced practice for long-term retention (Toppino & Gerbier, 2014). According to one prominent theory, repeating an item poten- tially reminds the learner of its prior occurrence, which prompts retrieving the previous presentation of the item, a process that enhances memory (e.g., Wahlheim, Maddox, & Jacoby, 2014; the next section elaborates on the effects of retrieving from memory). Massed repetition eliminates the retrieval process—there is no need to retrieve from memory because the same item was just presented. Another theory emphasizes the study/learning context (i.e., what surrounds an event, from the external environment to an individual’s mental state). With spaced repetitions, the context that gets encoded in memory with each presentation of an item is likely to be more variable (compared with massed repetitions that are close together in time and context); the variable con- texts that are stored in memory then serve as more effective cues for subsequent retrieval of the item (e.g., Glenberg, 1979). Deficient processing of massed repetitions is yet another theory. When a current item is the same as one that was just presented, the redundancy reduces attention (e.g., Magliero, 1983). The different theories are not mutually exclusive, and multiple mechanisms may act in concert to yield the memory advantage produced by spaced practice