In STEP 5 children are introduced to new graphemes for reading.
Some of these graphemes represent phonemes (sounds) that they have already learnt a grapheme for. For example, in STEP 3 children were taught 'ai' as the grapheme for the phoneme /a/ (as in train in the rain).
In STEP 5, children are taught that the phoneme /a/ can also be represented by the graphemes 'ay' (as in play in the hay) or 'a-e' (as in cake on a plate). This variation needs to be taught as it is common in the English language system.