Dysgraphia causes difficulty in writing (the act of getting thoughts onto the paper), handwriting (legibility) and spelling, and both of my boys have it (those on the Autism spectrum and those with ADD or ADHD can be especially prone to having it, although it is not limited to those two groups). I've done enough research on the topic to write a doctoral dissertation in an effort to help my children be at least functional writers.
This article is from All About Spelling and includes a plug for their products, but it also provides a very clear roadmap for how to help: http://blog.allaboutlearningpress.com/dysgraphia/
As far as my own efforts go, last year and this year we have used products from the Institute for Excellence in Writing for the writing process component. This year, we are using the Handwriting Without Tears App to help with letter formation and All About Spelling (starting with Level 1) to work on spelling.
I'm pleased with these products and the incremental progress we are making, but I honestly feel that even if I had these products a few years ago, it wouldn't have helped at that point. At that stage, almost every encounter with writing ended with a meltdown. At 11 and 13, both their brains and their personalities have matured. While they still complain about it on occasion and struggle with the process, they can recognize the value in learning how to write and spell.