Difficulties with Reading and Writing are common and can often coexist with other special needs such as ADHD and Autism Spectrum Disorders. Here are a couple resources with more information on Dyslexia and Dysgraphia:
Understanding Dysgraphia offers an overview of writing difficulties and some ways to help (while it is geared primarily towards students attending traditional school, the information can be a good starting point for homeschoolers).
Books Every Parent Should Read About Teaching Kids With Dyslexia– This is a list of books to help those teaching children with dyslexia from the Homeschooling with Dyslexia website.
Navigating Learning Disabilities and the Cost of Treatment – This article explains the prevalence of many common learning disorders and costs associated with them. It deals primarily with public school education but is interesting to read.
Assistive Technology for Learning Disabilities – This article offers a good overview of learning disabilities and some assistive technology that can be helpful.