In addition to interleaving and retrieval, an effective learning strategy is spaced practice. The opposite of cramming, spaced practice requires revisiting material over time. As early as the 1890’s a German psychologist described the “forgetting curve” and found how fast memory fades. He documented  a 50% memory loss after only 24 hours. “Practising or rehearsing slows down the forgetting process, with spaced practice much more effective than massed practice ( practice without spaces).” 

Spaced practice is related to a new theory of disuse: even previously strong memories fade with time if they are not used. Examples include a childhood friend’s name, and old family address or phone number. Thus, to reinforce information, spacing practice over  periods of time helps to place the material into long term memory. 

In addition, learning is also related to  the brain’s storage strength: “a measure of whether information is deeply embedded or well learned (is it likely to be recalled later?)” So re-reading a chapter is less effective than putting that material aside to focus on something else (interleaving), and then returning to the chapter.  

Spaced practice occurs over multiple short sessions. Dividing study into shorter intervals of approximately forty-five minutes instead of long sessions of five hours is a more effective method of storing information into long-term memory. The results of a meta-analysis indicated that “maximal retention increased as retention interval increased.” Thus, dividing the learning into shorter sessions, provides the opportunity to focus on fewer concepts in more detail while also reviewing the material from previous sessions. Repeatedly revisiting course materials over multiple sessions, results in encoding that information into long-term memory.  Over a century of research supports the positive effect of spaced learning.  So, incorporating this strategy, along with retrieval and interweaving, can result in better retention and more powerful learning.