Consider hiring a tutor. The classroom environment affords little direct attention by the teacher, and when it is given, the humiliation factor of being called on in class can reduce concentration, when it instead needs to be increased.
Tell the tutor what gaps you think there are. Consider what material needs to be drilled. For example, the student's multiplication tables may not be reflexive. This alone can keep a student from keeping up with the class discussion. An example of how math education builds on reflexive recall is reduction of fractions, which entails factoring, which in turn entails knowing the multiplication tables in reverse.
Encourage the tutor to drill one on one. Five minutes of drilling on a weak point with 30 skill-specific problems can be far more helpful than an hour of haphazardly doing problems start to finish---since the lesson is tailored to the student's weakness. Drills coming from a tutor are preferable to doing them alone, since dyscalculia is characterized by inattention.
Choose a skill-appropriate pace. Don't bite off more than you can chew. Because of the cumulative nature of math, going too fast can just kill morale and cause a mental shutdown that inhibits learning. Going slower is often better. Dwelling on one problem until one has it firmly in mind can serve as a useful mental prototype for future problems.
Expose yourself to a little math each day. Sometimes the material doesn't "take" when exposure isn't regular enough.