I’ve written elsewhere about how British psychologists at the MRC Applied Psychology Unit, now the MRC Cognition and Brain Sciences Unit, worked with the British Post Office to design the most memorable system of postcodes in the world. The Unit was also involved in other projects for the Post Office, primarily concerned with changes taking place in the way mail was sorted and distributed.
With the introduction of automated letter sorting and the inability of the system at the time to recognise handwriting, by the 1970s there appeared to be a need to either employ typists or teach current postal workers to type. Nowadays, of course, many people have developed at least a limited typing proficiency, but forty years ago it was standard practice to send hand-written documents to the ‘typing pool’ where skilled typists would do the job for you. Deciding not to employ an army of typists, the Post Office found itself in the position of having to teach some 10,000 postal workers to type.
The Spacing Effect
Cognitive psychologist Alan Baddeley saw this as an opportunity to examine the most effective ways to teach people a new skill. Ebbinghaus had already concluded that learning over a longer time was more efficient than over a shorter period, a finding conformed by Adolf Jost a few years later and leading to ‘Jost’s Law of Forgetting.’ Jost memorised sets of 12 syllables, all of which were repeated 24 times on other days but in different distributions. He found that he was better able to remember on the second day than on the first and on the third day better than the on the second, thus adding weight to the effectiveness of distributed (or spaced practice). In another series of experiments conducted between 1911 and 1912 at the University of Michigan, Nellie Perkins once more confirmed both Ebbinghaus’s and Jost’s earlier findings.
Other studies followed under the guise of Verbal Learning, defined as ‘the process of learning about verbal stimuli and responses, such as letters, digits, nonsense syllables, or words’, and described by Miller as ‘perhaps the dreariest area… of the whole of psychology’ (Baddeley, 2018 p85). Verbal learning studies would continue throughout the behavioural ascendency before being incorporated into cognitive psychology during the 1950s and ’60s. By the time the British Post Office had begun to mechanise, experimental psychologists, like Baddeley, were turning their attention to practical, real-world problems.
The Study
Baddeley, therefore, set about designing training schedules that could test the most appropriate time scales required to teach people to type. He decided on four conditions, the results of which could be compared for effectiveness. One group were given one training session of one hour per day, a second two sessions of one hour a day; fourth one session of two hours per day, and the final group, two session of two hours per day.
The most efficient schedule was found to be one session of one hour per day, while the least efficient were the two hour sessions. Distributed learning, therefore, was more effective than blocked learning. In addition, Baddeley asked participants to complete a questionnaire of how satisfied they had been with the sessions. Those in the one session, one hour per day group were the most dissatisfied, believing that they were learning more slowly despite being the most efficient group in the long-term.
The final point is interesting for several reasons, not least because it implies that distributed practice leads to fewer short-term gains but greater long-term gains and people may not be able to see progress over a shorter time scale.
The concept of distributed practice (or the spacing effect) is now becoming popular amongst teachers and other educators, a curious phenomenon when we consider that it dates back to late 1800s, with consistent findings since then. Nevertheless, most learning still tends to take placed in blocks (known as blocked learning, unsurprisingly). This might be, in part, due to uncertainty over timing and the desire for short-term results to the detriment of long-term gains.
Future Developments
Jonathan Firth at the University of Strathclyde (and my co-author on Psychology in the Classroom) has been doing some interesting work in this area, including this recent paper.
The Emotional Learner 
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