See the whole and both parts
A number bond shows how two parts join to make one whole. Read all the values you can see before deciding which circle is missing.
For a whole of 12 and one part of 5, the other part is 7 because 5 and 7 join to make 12. If the parts 5 and 7 are shown instead, their whole is 12.
Use the relationship both ways
When a part is missing, think about what joins the known part to make the whole. When the whole is missing, combine both parts.
Ask a child to point to the whole before calculating. This makes it easier to tell whether to find a missing part or combine two parts; the focused activity then practises both positions.