12 and 20
There is no reminder that 12 is a ‘teen’ number when we say its name and it can often become confused with both 20 and 21. This confusion can be reduced by focussing on how the numbers 11 and 12 follow on from 10, ideally before progressing to the ‘teen’ numbers and beyond. Using base 10 equipment or arrow cards will help a pupil to see how 10, 11 and 12 are made from one ten and an increasing amount of units. If a pupil is introduced to 20 before this is secured, they may learn to associate the ‘twe’ sound at the beginning of ‘twenty’ and ‘twelve’ with a 2, but be unsure of how to proceed.
Due to the repetition of the ‘teen’ sound when counting, pupils can also mistakenly say ‘twen teen ’ instead of ‘twen ty ’ when counting which further confuses the issue! The ‘ty’ in 20 must be reinforced and base 10 equipment can be used to show why 20 is not a teen number.