Mental strategies for addition and subraction

How important is mental calculation?

The ability to calculate mentally using a range of strategies is recognized as the basis of being numerate. It is a reasonable expectation that most pupils in primary schools should be able to learn to add and subtract using informal, mental strategies with three-digit numbers. This does not mean, of course, that they do not write anything down. They may need to write the question down for a start, so they don’t forget it – and it may be helpful to support their mental calculation with a few jottings along the way or with a picture such as a number line.

Remember to make it clear to pupils and parents  that there is no ‘proper’ way of doing calculation and that an effective mental or informal method is as valid as a formal written method.

It is now generally realised that most of the problems that pupils encounter in calculations in primary schools are associated with their being introduced too early to formal algorithms, written in a vertical format. Vertical layouts for additions and subtractions especially lead pupils to treat the digits in the numbers as though they are individual numbers and then to combine them in all kinds of bizarre and meaningless ways.