One of the most common difficulties in maths is with ‘teen’ and ‘ty’ numbers. There can be a confused ambiguity about these numbers which will become more deeply ingrained and difficult to correct the longer it goes unnoticed and which can greatly affect a pupil’s confidence and ability with number.

When we read and write numbers, we do so from left to right, just as we would words. So when reading or writing 42, we begin with the 4 tens before moving on to the 2 units. However, we cannot read and write ‘teen’ numbers in the same way. With 14, although we say or hear the four units first, then the ‘teen’, we have to read or write the 1 ten first, then the 4 units.

Some pupils need a lot of exposure to ‘teen’ numbers and repeated practice of reading and writing them, before they will be able to use them correctly. It is important that pupils say the ‘teen’ clearly and write the 1 ten first, to build confidence and fluency and to prevent future problems. Seeing that the ‘teen’ numbers follow on from ten, as they count on a numberline or a 100 square, will reinforce this. Where pupils are not secure with this, later confusion between numbers such as 13 and 31 will result.