Twenty problems a sheet, each written on one line with a box for the missing number: 7 + ___ = 12, or ___ + 5 = 12. The blank alternates between the first and second addend so a page cannot be finished by spotting a pattern.
A child who can answer 12 - 7 but stalls on 7 + ___ = 12 has learned subtraction as a separate procedure rather than as the other side of addition. That is what these sheets practise: that the two operations are one relationship read two ways, and the missing number can be found by counting up or by subtracting.
The number missing from an addition sentence - the box in 7 + ___ = 12. Finding it is the same skill as the subtraction 12 - 7, which is the point of practising it in this form.
First and second grade, alongside the addition and subtraction facts to 20. It is often the step that makes subtraction click.
Count up from the number shown to the total, or subtract the number shown from the total. Both give the same answer; which one feels natural is a good sign of how the facts are understood.
Yes. Turn on Include Answer Pages and the key prints each equation complete, with the number that belonged in the box filled in.