The spacing effect: A case study in the failure to apply the results of psychological research.

The spacing effect would appear to have considerable potential for improving classroom learning, yet there is no evidence of its widespread application. I consider nine possible impediments to the implementation of research findings in the classroom in an effort to determine which, i f any, apply to the spacing effect. I conclude that the apparent absence of systematic application may be due, in part, to the ahistorical character of research on the spacing effect and certain gaps in our understanding of both the spacing effect and classroom practice. However, because none of these concerns seems especially discouraging, and in view of what we do know about the spacing effect, classroom application is recommended. The spacing effect--which refers to the finding that for a given amount of study time, spaced presentations yield substantially better learning than do massed presentationsmis one of the most remarkable phenomena to emerge from laboratory research on learning. It is remarkable in several respects. First, the spacing effect is one of the most dependable and replicable phenomena in experimental psychology. Second, it is remarkably robust. In many cases, two spaced presentations are about twice as effective as two massed presentations (e.g., Hintzman, 1974; Melton, 1970), and the difference between them increases as the frequency of repetition increases (Underwood, 1970). Moreover, demonstrations of achievement following massed presentations often are only slightly higher than that following a single presentation (e.g., Melton, 1970). Third, the spacing effect is truly ubiquitous in scope. It has been observed in virtually every standard experimental learning paradigm, with all sorts of traditional research material (Dempster, 1987a; Hintzman, 1974; Melton, 1970). With all of these characteristics in its favor, the spacing effect would seem to have considerable potential for improving classroom learning. However, there is little evidence that this potential has been realized. Neither American classrooms nor American textbooks appear to implement spaced reviews in any systematic way, and by comparison, Soviet mathematics textbooks provide a much more distributed method of presentation than do their American counterparts (Stigler, Fuson, Ham, & Kim, 1986). Nor is there much evidence that the next generation of educators is being better informed. In a recent sampling of practitioner-oriented textbooks suitable for use in teacher education programs, I found either little or no mention of the practical benefits of the spacing effect, and in some cases the spacing effect was confused with other phenomena (e.g., Good & Brophy, 1986; Mayer, 1987; Slavin, 1986; Woolfolk, 1987). One wellknown educator, in fact, advised against spaced practice at least in the early stages of learning (Hunter, 1983). Why is it that research findings that appear to have significant implications, such as the spacing effect, often are not utilized by teachers and curriculum makers? In general, the problem is that there is no well-developed implementation model, nor is there a standard methodology for analyzing the conditions that foster the transfer of knowledge from the laboratory to the classroom (see Hosford, 1984, for a discussion). Obviously, issues regarding the utilization of findings from basic research are complicated, and there are many potential impediments to the implementation of research findings in the classroom. In this article, I explore nine potential impediments, all of which seem reasonable at first glance, in an effort to determine which, if any, apply to the spacing effect. Impediments to Application The Phenomenon Has Not Been Known Long Enough Although the time lag between discovery and application varies greatly, some considerable period of time often intervenes between the publication of research findings and their application. In the case of the spacing effect, however, a considerable period of time already has passed since its initial documentation. The spacing effect was known as early as 1885 when Ebbinghaus published the results of his seminal experimental work on memory. With himself as the subject, Ebbinghaus found that for a single 12syllable series, 68 immediately successive repetitions had the effect of making possible an errorless recital after seven additional repetitions on the following day. However, the same effect was achieved by only 38 distributed repetitions spread over three days. On the basis of this and other related findings, Ebbinghaus concluded that "with any considerable number of repetitions a suitable distribution of them over a space of time is decidedly more advantageous than the massing of them at a single time" (Ebbinghaus, 1885/1913, p. 89). Jost, also working with nonAugust 1988 9 American Psychologist Copyright 1988 by the American Psychological Association, Inc. 0003-066X/88/$00.75 Vol. 43, No. 8, 627-634 627 sense syllables, reported similar findings and in 1897 formulated what was to become known as Jost's Law: "If two associations are of equal strength but of different age, a new repetition has a greater value for the older one" (McGeoch, 1943, p. 140). In 1928, Ruth published a review of dozens of studies of the spacing effect. Although interpretation of the results of these studies (e.g., Dearborn, 1910; Perkins, 1914; Pyle, 1913; Starch, 1912) is complicated by other, potentially confounded variables, the results tend, in general, to confirm the earlier work by Ebbinghaus and by Jost. Thus, published reports of the spacing effect have been in existence since the latter part of the 19th century and the early part of the 20th century. The Phenomenon Has Not Received Recent Documentation In the absence of recent documentation, research findings may seem stale or anachronistic, but, as most, if not all, students of the learning literature know, the spacing effect has been well-documented in recent times. Many studies of this phenomenon were published during the 1960s and the 1970s, as reviews by Hintzman (1974), Melton (1970), and Glenberg (1979) attest. Although much of the research included in these reviews was reminiscent of the work of Ebbinghaus in using easily analyzable simple verbal units, the fruits of this research are considerable from any perspective. For example, the ubiquitous, highly replicable character of the spacing effect fostered the notion that its existence must be telling us something important about memory (e.g., Hintzman, 1974). Also, it deafly demonstrated that the Total Time Law, which states that the amount learned is a direct function of study time regardless of how that time is distributed, was in deep trouble or at least in need of a major overhaul (Melton, 1970; Underwood, 1970). More recently, the spacing of repetitions has been the subject of studies reported in a variety of journals, including some with an applied perspective (Bahrick & Phelps, 1987; Cuddy & Jacoby, 1982; Dellarosa & Bourne, 1985; Dempster, 1987b; Elmes, Dye, & Herdelin, 1983; Glenberg & Lehmann, 1980; Glover & Corkill, 1987; Toppino & DiGeorge, 1984; Toppino & Gracen, 1985). Thus, documented evidence of the spacing effect has appeared in the literature continually for the past 100