This study focused on children’s use of the direct subtraction (DS) and indirect addition (IA) strategy when mentally solving subtractions in the number domain up to 1000, taking into account their working memory (WM). Sixty-nine 6th-graders participated in 3 sessions, and each time they solved an Arithmetic Task and a WM Task. All Arithmetic Tasks consisted of 10 subtraction problems (5 DS-problems; 5 IA-problems) and were offered in 1 choice condition (children could choose between DS and IA on each subtraction) and 2 no-choice conditions (they had to use either DS or IA). The IA-strategy was used frequently and efficiently. No effect of WM was found on frequency; efficiency analyses showed an interaction between condition, problem type and WM group only for accuracy, not for speed. Surprisingly, only children with lower WM capacities fitted their strategy choices to their individual strategy speed abilities. We will discuss the theoretical, methodological, and instructional implications.status: publishe
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