Decodable readers are considerably different from levelled readers (A books, B books, C books, etc.), which many reading programs in the past have used. 

Decodable readers focus on the sound/letter connection that makes up the "alphabetic code" used in languages. Decodable books use words that can be sounded out once a student has learned the sound/letter knowledge that connects to the words in the book. (Please see the "Home Page" for examples of decodable words.) When the task is identify a word, the focus needs to be the letters in the words. This will build the ability to to automatically recognize MANY words over time. The intentional work decoding of words leads to automatically remembering the letter sound connection, and later, the automatic knowledge of words. This instant recognition of the letters and sounds, and then words, is called orthographic mapping.

'Levelled' readers focus almost exclusively on 'meaning' and simple memorization of whole words and sentence patterns. Levelled readers teach children to rely on multiple cues in the text or pictures to guess unknown words and/or memorize a list of the most common words in print. Predictive and repetitive sentences help students predict the correct words and read them as a whole unit (e.g., "I get my lunch. I get my books. I get my shoes. I get my sweater. I go to school."). This type of whole word reading can interrupt the orthographic mapping process, leading to developing inefficient reading strategies for emergent readers.