Decodable books, also known as phonic readers, are books that contain words only using a range of phonemes that children have learnt and known tricky words. These phonemes are gradually introduced (starting with s, a, t, p) using a week-by-week progression. Decodable books also use a small number of common exception words (or tricky words) also introduced gradually. The first books in phases 2 and 3 have simple CVC (consonant vowel consonant words) e.g. hat, bat tip. As children progress, they encounter more complex words with the full range of phonemes that children have learnt.