When using a Systematic Synthetic Phonics programme decodable readers will align with the grapheme-to-phoneme correspondences taught. Therefore, the text is decodable to the child, depending on which correspondences they can blend.
They will be shown by the author.
If the systematic synthetic phonics programme follows the Letters and Sounds program then the books will align with the GPC teaching order. Each book ONLY has these graphemes, and a few high-frequency words (the, is, was etc) The phonics books will show the graphemes and words, so everyone knows which the child will need. These decodable readers are often organised into phonics code levels or phases.
In Letters and Sounds Phase 2, letters (graphemes) and their commonly used 'sounds' are introduced one at a time.
Set 1: s, a, t, p
Set 2: i, n, m, d
Set 3: g, o, c, k
Set 4: ck, e, u, r
Set 5: h, b, f, ff, l, ll, ss
As soon as each set of graphemes is introduced students use these to blend eg s-a-t are used to read and spell the word 'sat'.
Within the Speech Sound Pics Approach the following grapheme-to-phoneme correspondences are introduced, in line with Letters and Sounds. Use the free Code Level readers and the Spelling Piano app to learn to read and spell with these correspondences in Kindergarten / Reception. So this Purple Code Level reader only has s a t p i n m d g/g o c/c k ck e u r h b f l le ll ss and a few high-frequency words. The students can practise blending, as they know the graphemes. They do not need to guess from 'first sound', miss out words or use the illustrations to figure out the words.