In the formal column method for both addition and subtraction, it’s vital that numbers are set out correctly to maintain their place value. However, as pupils usually write from left to right, they can sometimes find this difficult.
For example, setting out the calculation 236 + 79 may result in:
The 9 in the bottom number must be aligned directly beneath the 6 in the top number, as both digits represent units. Some reinforcement of place value may be necessary for pupils to understand why.
In the last two examples, a zero has been inserted to make both numbers line up. The pupil needs encouraging to read the number in the question then the number they have written, to recognise that they are not the same.