Interleaving Helps Students Distinguish among Similar Concepts

When students encounter a set of concepts (or terms or principles) that are similar in some way, they often confuse one with another. For instance, they might mistake one word for another word with a similar spelling (e.g., allusion instead of illusion) or choose the wrong strategy for a mathematics problem because it resembles a different kind of problem. By one proposition explored in this review, these kinds of errors occur more frequently when all exposures to one of the concepts are grouped together. For instance, in most middle school science texts, the questions in each assignment are devoted to the same concept, and this blocking of exposures ensures that students need not learn to distinguish between two similar concepts. In an alternative approach described in this review, exposures to each concept are interleaved with exposures to other concepts, so that a question on one concept is followed by a question on a different concept. In a number of experiments that have compared interleaving and blocking, interleaving produced better scores on final tests of learning. The evidence is limited, though, and ecologically-valid studies are needed. Still, a prudent reading of the data suggests that at least a portion of the exposures should be interleaved.  Note Address correspondence to Doug Rohrer, Department of Psychology, PCD 4118G, University of South Florida, Tampa, FL, 33620, drohrer@usf.edu. I thank Pooja Agarwal and one anonymous reviewer for their comments on an earlier version of this review. This work was supported by the Institute of Education Sciences, U.S. Department of Education, through Grant R305A110517 to the University of South Florida (PI: D. Rohrer). The opinions expressed are those of the author and do not represent views of the Institute or the U.S. Department of Education. In virtually any academic discipline, students encounter each important concept more than once, and creators of textbooks and other kinds of learning materials must therefore decide, incidentally or otherwise, how these exposures will be arranged. For example, a science class assignment might focus on a single principle (e.g., photosynthesis) or cover multiple principles. These kinds of scheduling decisions are often dismissed as inconsequential or even dull, which might explain why this kind of intervention receives little or no attention in textbooks and courses devoted to curriculum and instruction. Yet the timing of learning exposures can dramatically affect learning outcomes. Many experiments have shown that merely rearranging the order in which students encounter examples or questions, without altering the number or nature of these exposures, can boost scores on final tests of learning. This review examines one kind of scheduling intervention that appears to be especially useful when students must learn to distinguish among similar concepts. Discrimination Learning When students must learn to distinguish among similar concepts, they often confuse one with the other. For example, biology students are asked to distinguish among the genetic processes of transcription, transduction, transformation, and translation – four terms with similar spellings and meanings. Not surprisingly, a greater degree of similarity makes the task more difficult (e.g., Skinner, 1933). A failure to distinguish, or discriminate, between two concepts (or terms or principles or stimuli) is called a discrimination error, and learning to make these distinctions is discrimination learning. The genetics example is obviously cherry picked, and that raises a question that underlies the practical significance of this review: how often must students make difficult discriminations? Indeed, most of the research on discrimination learning examines skills or concepts learned outside the classroom. For instance, there are many studies of the subtle discriminations made during speech comprehension (e.g., “pa” vs. “ba”) and face recognition, but children typically master these skills before they begin school. In other studies of discrimination learning, subjects learned skills needed only by experts, such as distinguishing among different species of birds. This is not to say that discrimination expertise is necessarily impractical – indeed, medical doctors must learn to distinguish among diseases with similar symptoms. Still, the majority of discrimination