The section above, on phonological awareness, stated that phonological awareness skills are believed to be indispensable to reading and spelling skills. This section will explain this relationship.
English is written with an alphabet. The defining characteristic of an alphabet is that it uses its written symbols to stand for the individual sounds, or phonemes, that make up words (this is the alphabetic principle). Someone learning to read or write an alphabetic system must grasp this basic insight to really understand how the writing system works. In order to be able to grasp this notion, however, a person has to know about individual sounds in words--the person has to have phonemic awareness. If a person does not realize that words are made up of individual sounds, that person has nothing to associate with the written symbols of the alphabet. The person without phonemic awareness can only memorize the image of each written word.
I once witnessed a dramatic demonstration of this situation. I was visiting a friend whose son was in the early months of first grade at the time. The child was apparently not getting any phonemic awareness training, and so was only learning how words are written one by one, memorizing each word independently of all the others. The father and I were working through a homework assignment with the child. There was a page with rectangles on it; above each rectangle was the name of a color: black, blue, white, red, etc. The instruction was to color in each rectangle with the color named by the word. The child was supposed to read the color name, then choose the correct crayon and color the box.
This child guessed randomly at the color names. Upon seeing the word 'black', the child guessed 'white'. When asked about the sounds associated with the 'bl' of 'black', or the 'w' of 'white', the child stared at us blankly. The child did not notice the similarity between the beginnings of the words 'black' and 'blue'. This was not a child of below-average intelligence (if anything, the opposite was true), and the child was not socioeconomically disadvantaged--his family was quite affluent. The problem was that the literacy training the child was getting introduced him to neither the phonemic makeup of words nor the regular sound-symbol correspondences of English spelling. He was unable to decode simple words.
This event seems bizarre to literate adults like you and me, for whom sound-letter relationships are deeply entrenched from years of education and reading. But it is a stark reminder of how foreign the notion of writing is to an illiterate child, even a child who speaks very fluently. Essential to decoding and independent reading is awareness that written symbols stand for individual sounds. Essential to understanding this idea is knowing that a word is a string of individual sounds. Hence the crucial importance of phonemic awareness.