"When phonics instruction is introduced after students have already acquired some reading skill, it may be more difficult to step in and influence how they read, because it requires changing students' habits.
For example, to improve their accuracy, students may need to suppress the habit of guessing words based on context and minimal letter cues, to slow down, and to examine spellings of words more fully when they read them. Findings suggest that using phonics instruction to remediate reading problems may be harder than using phonics at the earliest point to prevent reading difficulties."