Key Words are the most frequently occurring words in the English language and research has shown that a few of these key English words form a high proportion of those in everyday use. The Key Words with Peter and Jane books introduce the key words gradually and then repeat them frequently, thereby building confidence in children when they recognise these key words on sight. There are 12 levels in the scheme, each with 3 books (a,b,c). Series a gradually introduces and repeats new words; series b provides further practice of these same words but in a different context and with different illustrations; series c invites children to try writing the words and introduces reading using phonics, allowing them to decode increasingly difficult words.