Addition and Subtraction to 100

Method

1. Start concrete: model the calculation with real bundles of ten straws (or ten-sticks) and single ones, physically adding or removing a bundle or a single item.
2. Move to pictorial: draw an empty number line, mark the starting number, then draw jumps of ten followed by jumps of one to reach the answer, so the child sees the size of each step.
3. Only then go abstract: write the same working as a partitioned number sentence, e.g. 34 + 25 = 34 + 20 + 5.
4. For addition, always jump in tens first, then in ones, so the child deals with the bigger, easier steps before the fiddly small ones.
5. For subtraction, encourage counting UP from the smaller number to the larger one when the numbers are close together, and counting BACK when they are far apart, since each is more efficient in its own situation.
6. Check every answer using the inverse: if addition gives an answer, subtract one of the added numbers back off, and it should return the number you started with.
7. Watch for the classic misconception where children add the tens and ones correctly on their own but then recombine them wrongly, for example working out 40 + 20 = 60 and 3 + 4 = 7 correctly, then writing the final answer as 607 instead of 67, because they string the two results together rather than adding them.

Practice questions

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Free printable worksheet