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Overview
Overview
Algorithms for addition and subtraction are in the Ontario curriculum expectation for the first time in Grade 3.
However, even once students know those algorithms, they should be encouraged to use some of the other strategies mentioned in the Working with Numbers section of this website (e.g. compensating, taking jumps of 10, overshoot and return).
For example, if students are asked to calculate 1002 – 998, the standard subtraction algorithm is not the quickest way to find an answer, and indeed using it often leads to incorrect answers.
Supporting Students with efficient strategies
Supporting Students with efficient strategies
One important visual to support students in using efficient strategies (and being able to communicate them) is the open number line.
An open number line is a number line with no preset marks or numbers on it. It serves to record teacher or student thinking.
Efficient strategies on the open number line.mp4In later grades, compensation in subtraction can be a really helpful strategy. We often ask students to imagine they have an amount of money, and can spend it on different items. However, they often make errors calculating this using the standard algorithm.
If they use "compensation", they can subtract 1 cent from the start amount, and one from the amount they spent. This is a much simpler calculation, and the answer is correct.
Games to Promote Efficient strategies
Games to Promote Efficient strategies
A modified version of the traditional "war" card game. This game provides a wider range of 'known facts' to be used to determine the sum of the two cards flipped. (Lawson; pg. 176).
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