The best way to teach children to read has been a long running controversy in education. While many advocated the top-down approach and others support the bottom-up model, the best strategy probably includes a happy medium of both approaches.
In the top-down approach, the student's reading is influenced by their previous knowledge and expectations. Many educators emphasize that this strategy can help struggling readers because the brain naturally anticipates which words the reader will process next and takes in only enough visual cues to confirm their anticipatory guess or hypothesis. In this kind of model, reading becomes a "psycholinguistic guessing game" (qtd. in Blackwell Guide to Linguistics). One advantage to the top-down reading theory is that the brain processes the words faster, increasing reading speed.
One disadvantage of this approach to reading is that while students "train" their brain to anticipate words and fill in the gaps, it can result in an incomplete reading of the text, especially if the students skip important words or incorrectly guessed on the completion of thoughts or phrases, whereas in the bottom-up approach, students use each word to build meaning.
Treiman, Elizabeth. "Reading." Blackwell Guide to Linquistics. Blackwell, 2001. Web. 17 Jan. 2013.