For parents
Adding with doubles: from 6 + 6 to 6 + 7
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If your child knows that 6 + 6 = 12, they already have a starting point for 6 + 7. Instead of counting every object again, look for the familiar calculation inside the new one and identify exactly what changes.
Start with two equal groups
Doubling means adding a number to itself. Make two rows of six blocks, one below the other. There are twelve blocks: 6 + 6 = 12. If the answer is not familiar yet, let your child count them. This strategy uses a known double; it does not require guessing or answering against a timer. Smaller groups such as 3 + 3 are a useful starting option.
Turn 6 + 6 into 6 + 7
Add one differently coloured block to the second row. The first row still has six, while the second now has seven. Two sixes make twelve, and the extra block adds one: 6 + 7 = 6 + 6 + 1 = 13. Point to that one on the table. Nothing was added to the first row: only one of the two addends changed.
You can start with the larger double
If your child remembers 7 + 7 = 14 more easily, build two rows of seven and remove one block from the first row. You now have 6 + 7, so 14 − 1 = 13. Both routes work. Ask which double felt more useful. There is no need to use both methods for every question; comparing them once can show why the adjustment changes direction.
Play a two-bay loading game
Draw two loading bays on paper and use blocks as parcels. Make number cards from two to eight. A parent picks a number and puts that many parcels in each bay. The child finds the total; then the parent adds one parcel to one bay. The child gives the new calculation and explains the change. Swap roles after three rounds. If an answer is uncertain, check the blocks together.
Four questions with answers
1. Find 4 + 5. Use 4 + 4 + 1 = 9. 2. Find 7 + 8. Use 7 + 7 + 1 = 15. 3. Find 8 + 7 using the larger double. Use 8 + 8 − 1 = 15; changing the order of addends does not change their sum. 4. Is 6 + 8 the same as 6 + 6 + 1? No: the difference is two, so 6 + 6 + 2 = 14.
When adding one is the wrong adjustment
“Double and add one” works for neighbouring whole numbers when you double the smaller number. If you double the larger, subtract one instead. For 6 + 8 the adjustment is two; for 6 + 6 no adjustment is needed. A common mistake is doubling seven in 6 + 7 and then adding one. Ask your child to point to the extra or missing block rather than repeat a rule without checking it.
Continue with Otto Math
Finish by asking your child to invent an addition question that uses a familiar double. A parent can then choose a short addition route in Otto Math and invite the child to explain their chosen calculation strategy. The app is available on the App Store for iPhone and iPad. Five routes in each book are free; Otto Plus unlocks the remaining routes.