Abstract
The subtraction-as-addition strategy (e.g., using the known sum 7 + 4 = 11 to solve for the unknown difference of 11 − 4 = ?) is an important example of mathematical reasoning and can facilitate subtraction fluency. A 12-weeks long randomized control trial consisting of an experimental group (structured-subtraction instruction/practice on the strategy) and two comparison groups (unstructured practice of subtraction combinations and structured instruction/practice on a different reasoning strategy) served to evaluate whether conceptually based instruction was efficacious in promoting knowledge and reliable use of the subtraction-as-addition reasoning strategy. Eighty-one Grade K-3 students (mean age 7.9 years) participated. A computational shortcut task (presenting a related sum such as 7 + 7 = 14 before 14 − 7 = ?) was used to gauge whether participants recognized addition could be used to solve related, unpracticed, and unknown subtraction combinations. Significantly more participants in the structured-subtraction group than those in the comparison groups used a related sum to avoid computing a difference. A large majority of participants in the experimental group, but not in the comparison groups, exhibited knowledge and reliable use of the subtraction-as-addition strategy.
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