The study, published in Psychological Science, suggests the optimal amount of time during which learning should take place depends on how long the information needs to be retained.

Hal Pashler and John Wixted of the University of California, San Diego, said that while the finding that greater spacing between study sessions can enhance later memory was expected, some results of the study of 1,000 study subjects are new.

"First, the study used much longer time intervals than in prior research, and it turned out that effects were larger than those seen in earlier studies using much shorter time periods," Pashler said in a statement. "Second, the longer the final retention interval, the longer the optimum delay between study and review."

Pashler advises students, "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."

Cramming is not recommended by the researchers. Packing "a lot of learning into a short period is likely to be extremely inefficient," Pashler says.