Running Head: A TRIAL OF MENTAL ABACUS INSTRUCTION

Mental abacus (MA) is a technique for performing fast, accurate arithmetic using a mental image of an abacus; experts exhibit astonishing calculation abilities. Over 3 years, 204 elementary-school students (age-range at outset: 5-7 YO) participated in a randomized, controlled trial to test whether MA expertise (a) can be acquired in standard classroom settings; (b) improves students' mathematical abilities (beyond standard math curricula); and (c) is related to changes to basic cognitive capacities like working memory. MA students outperformed controls on arithmetic tasks, suggesting that MA expertise can be achieved by children in standard classrooms. MA training did not alter basic cognitive abilities; instead, differences in spatial working memory at the beginning of the study mediated MA learning.