I am a 4th grade teacher and your post sounds like your child has difficulty geting his ideas from his head to his paper, not dysgraphia...I have taught many students with it and it is not the same as what many call "writers block".
Writing is probably the most difficult skill to teach/learn b/c there is no code/trick/formula to it. It takes a lot of modeling. To be a good writer you ahve to be exposed to good writing.
Most students just don't know where to begin. Writing is so broad even when given a specific topic. Don't feel that your child is behind b/c writing, beyond sentences and simple paragraphs is a 4th grade skill. In most states, 4th grade is the year for writing development. Most 4th graders read well above their writing level. I often have students that can read on a 6th grade level and struggle with 3rd grade level writing b/c reading has a code to break and tricks to solve.
I start my students off with writing frames and graphic organizers. Basically, a graphic organizer provides a visual tool to organize ones thoughts and gives them a starting off point. Writing frames give sentence starters for the required parts of the essay/paragraph. there are generic ones you can use with most writing pieces and you can also make your own. I'd be happy to help you but I would need more specifics. If you want to give me your email I could send you examples. Unfortunately, my DH is on the main computer which has some of my work stuff, but most is at my computer at work, but I could get around to it tomorrow. Let me know...school doesn't start for me until next week so I have some spare time...
There are some great books for "teachers" that help with writing. Craft Lessons and Nonfiction Craft Lesson both by Ralph Fletcher are great resources.
Also, what type of school does he go to...public, private, alternative? What does your child read independently?
Hope this helps...
Mama to Jack (12/7/06) & Liam (4/3/08) & Iris Hope (10/6/10)