If the method you have been using isn't working, consider trying something new. What a child needs is not more drills, but an intentionally different approach. We should abandon the notion that the child is broken and cannot learn; rather success is much more likely if we adjust the way we teach.
Over the past ten years, I have learned about a whole array of classifications for disabilities. There are so many! One could get the impression that children are getting more and more broken, and we are developing more and more detailed labels for describing them.
It helps to understand ahead of time what will be hard for struggling readers. After working with struggling readers for several years and taking the time to consider what they have in common, I have come up with a list of skills that are hard for them.