How to Teach Subtraction Facts: Think Addition

Why counting back goes wrong

Try 13 − 8 by counting back on your fingers: eight steps, backwards, keeping track of two things at once. It's easy to be off by one, especially when a child counts the 13 itself. The more steps, the more chances to slip. Children who rely on it often find subtraction harder than addition, and it's the method, not the child, that's the problem. Save counting back for small takeaways, like the minus 1 and minus 2 facts.

Teaching think addition

Start with real objects. Hide 3 of 8 blocks under a cup and ask how many are hiding. Children work that out by thinking 5 and what make 8? That's the idea. Then use the fact family triangle: cover a number and ask what's missing. Read subtraction aloud both ways: 13 take away 8, and 8 and what make 13? Over time, the second question becomes the habit.

Three other tools

When the numbers are close, like 12 − 9, count up from the smaller number: it's only 3 hops. When the fact crosses 10, like 14 − 6, stop at 10: take 4 to reach 10, and then 2 more. And when it's half of a double, like 16 − 8, use the double: 8 + 8 = 16, so 16 − 8 = 8. Most of the subtraction facts fall to one of these or to think addition.

How to do it with Sumtown

1. Make sure number bonds to 10 are solid. They're the base for all of this.
2. Work on fact families with the triangle.
3. Play the subtraction game, or lock it to one number, like minus 9.
4. Print a fact family sheet for a quiet five minutes.

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