ABSTRACT
This chapter focuses on developing strategies and algorithms for subtraction. There are two meanings for subtraction—take-away and distance—and there are four main categories of strategies: decomposing and recomposing by place value; decrementing by place value; finding the difference; and constant difference. Visual models, place value, properties of operations, and the relationship between addition and subtraction all play an important role in the development of strategies and algorithms for subtraction. Students should have both efficient strategies and algorithms for subtraction towards developing procedural fluency. When students look at the numbers first to decide on the best strategy for deriving the solution, they are approaching calculations strategically and flexibly. There is a danger in introducing a standard algorithm before developing understanding through strategies based on understanding. Students who are reliant on a procedure without understanding are at a disadvantage, as the procedure is subject to deterioration and errors are more likely.
