“Is Expanded Retrieval Practice a Superior Form of Spaced Retrieval? A Critical Review of the Extant Literature”, 2015 (; backlinks; similar):
The spacing effect is one of the most ubiquitous findings in learning and memory. Performance on a variety of tasks is better when the repetition of the to-be-learned information is distributed as opposed to massed in presentation. This observation was first formalized in Jost’s law, which states that “if two associations are of equal strength but of different age, a new repetition has a greater value for the older one” (1943). Spacing effects occur across domains (eg. learning perceptual motor tasks vs. learning lists of words), across species (eg. rats, pigeons, and humans), across age groups and individuals with different memory impairments, and across retention intervals of seconds to months (see et al 2006; 1976; 1996, for reviews).
In this light, it is interesting that spacing effects have not received much attention in Cognitive Psychology textbooks. In fact, in our sampling of 7 such textbooks, only one had a section dedicated to this topic, while virtually all cognitive text-books discussed mnemonic techniques such as the pegword or method of loci. Given the power and simplicity of implementing spaced practice, we clearly hope this changes in the future.