Ask them to repeat what you said. If they take notes, allow them to finish writing before you continue talking. The supervisor must be sure the employee understands. The employee has difficulty writing. This employee may find working with the supervisor on and outline of the assignment to be helpful.
Computers can be crucial.
Software which checks spelling and grammar is useful. Arrange to have someone proofread their work. The employee does not manage their time well. Many LD and ADD employees lack an inner sense of time. The LD or ADD employee may come in late and work past breaks and quitting time.