The younger a child is when an intervention is introduced the more likely it will be successful. Some school systems have screening programs starting in first grade to find at risk children. Those who are at risk are separated out for intensified instruction.
Unfortunately those that truly have dyslexia may not be identified for several years wasting precious time.
Recognize that dyslexia is fundamentally a brain-based issue with attaching sounds to letters and words. Because of this traditional phonics-based techniques may not work well with a dyslexic child. With phonics a child is being instructed at an inherent weakness.
Try the Free Dyslexia Screening from Reading Success Lab
These exercises are not phonics-based. They promote sight recognition of words and math facts circumventing the issues that often block a dyslexia reader from learning to read.