Elementary math in elementary school: The effect of interference on learning the multiplication table

Memorizing the multiplication table is a major challenge for elementary school students: there are many facts to memorize, and they are often similar to each other. This similarity creates interference in memory. Here, we examined whether learning would improve if the degree of interference is reduced, and which memory process are responsible for this improvement. In a series of 16 short training sessions over 4 weeks, first-grade children learned 16 multiplication facts – 4 facts per week. In 2 weeks the facts were dissimilar from each other (low interference), and in 2 control weeks the facts were similar (high interference). Learning in the low-similarity, low-interference weeks was better than in the high-similarity weeks. Critically, this similarity effect originated in the specific learning context, i.e., the grouping of facts to weeks, and could not be explained as an intrinsic advantage of certain facts over others. Moreover, the interference arose from the similarity between facts in a given week, not from similarity to the previously-learned facts. Similarity affected long-term memory – its effect persisted 7 weeks after training has ended; and it operated on long-term memory directly, not via mediation of working memory. Pedagogically, the effectiveness of the low-interference training method, which is dramatically different from currently-used pedagogical methods, seems to call for reconsideration of the way we teach the multiplication table in school.