Fig.1. The Forgetting Curve. Ebbinghaus (1885)
'The psychological conclusion demands a distribution of repetitions such that some of them should be produced at a later time, separated from the first repetition by a pause'. (Vygotsky, 1926)
More recently, in the last ten years in fact, Dr B Price Kerfoot of Harvard Medical School (2006) created a platform called SpacedEd (now Qstream) that uses multichoice questions, typically and most successfully with first year medical students, where sets of questions are randomised then sent out as text or email to tackle, I suppose, what Ebbinghaus (1885) identified with his 'Forgetting Curve'. An evidence based paper on the effectiveness of 'spaced learning' showed how there was better retention three months, six months and a year down the line.
Ebbinghaus, H (1885) Memory: A contribution to experimental phsychology.
Kerfoot, B, P (2006) SPACED EDUCATION. Interactive Spaced-Education to Teach the Physical Examination: A randomized Controlled Trial.
Vygotsky, L (1926) Educational Psychology