By analyzing what students have written, it's possible to determine what part of reading they're struggling with. For instance, it could be that a student doesn't hear the two sounds in a blend (ch, th, sh) and only hears it as one sound. It's fairly common for students not to hear the end of words and write the word: wate (for water) or col (for cold). Because reading is learned, partially through auditory skills, what and how a student "hears" words is key to teaching them the skills necessary to read for comprehension.
There are specific steps to learning how to read. First, learning letter recognition and the letter's sound, then learning words, then phrases, etc. Each of these steps require numerous repetitions (practice) so that the information becomes automated. When automation is achieved, the student no longer requires as much brain power to read certain words. This frees up the brain to better comprehend what is read.