I ought to state from the outset that, in my opinion, the academic writer most worth reading on this subject is the Emeritus Professor of Psychology at the University of South Florida, Diane McGuinness. Her Early Reading Instruction (2004), Language Development and Learning to Read (2005) and Why Children Can’t Read (1996) have all had an enormous influence on the way we teach reading and spelling. What's more, she writes with a clarity that many other academics can only dream about.
In her chapter 'On the nature of writing systems' in the first of the aforementioned books, she makes several fundamental points, the first of which is that '[a] writing system is a code in which specific elements of a language are mapped systematically to graphics signs or symbols'. In the case of English, the specific elements of the language to be encoded are the speech sounds: these, as McGuinness puts it, 'are the basis for the code, and the letters are the code'.
Unlike, say, Italian or Spanish, the English orthographic code is complex – there are many ways of spelling most sounds in the language and most spellings represent a number of sounds. As a consequence, it shouldn't be left to children to work out the code for themselves. If children (or illiterate adults for that matter) are to be taught to read and spell successfully, they need systematic instruction, properly taught by properly trained teachers. And, as I've argued before, the teaching should not be 'time-limited'.
If the Diane McGuinness prototype for the teaching of reading and spelling were to be adopted throughout the English-speaking world, illiteracy would be an unfortunate historical aberration.