See: Researchers report on the smart way to study
The results suggest, Pashler said, the optimal amount of time over which learning should take place depends upon how long the information needs to be retained: "If you want to remember information for just a week, it is probably best if study sessions are spaced out over a day or two. On the other hand, if you want to remember information for a year, it is best for learning to be spaced out over about a month."
Extrapolating from the results, he added, "it seems plausible that whenever the goal is for someone to remember information over a lifetime, it is probably best for them to be re-exposed to it over a number of years."
"The results imply," said Pashler, "that instruction that packs a lot of learning into a short period is likely to be extremely inefficient, at least for remembering factual information."
