When reading and writing the numbers 13 and 15, it isn’t always obvious to a pupil how the units digit corresponds to how we say the number. As well as having to identify whether the number is a ‘teen’ or ‘ty’ number, they also have to work out which ‘teen’ or ‘ty’ number it is.

When we say the number 14, we can hear the ‘four’. However, when we say 13, we hear ‘thir’ which isn’t a recognisable number. Likewise, in 15 we hear ‘fif’. Differentiating between 13 and 15 can be even more difficult for pupils with speech or hearing difficulties, particularly as the ‘th’ sound is often mispronounced as ‘f’.

The link between the ‘thir’ sound and 3 and the ‘fif’ sound and 5 can be reinforced by using base 10 equipment or arrow cards to make these tricky numbers, and by using a numberline to support counting. Being able to make this link will then allow pupils to correctly identify all the numbers in the 30s and 50s . Beyond this, it will also enable pupils to link the words ‘third’ and ‘fifth’ to 3rd and 5th, and later on, to understand thirds and fifths as fractions.