OP, here are some examples of strategies/things that can be used in the classroom in terms of accommodations:
http://www.ldinfo.com/dyscalculia.htm#top
http://www.eduplace.com/graphicorganizer/
Also keyboarding when he's ready for it. Keep fighting for your kid--squeaky wheel gets the grease. Who cares what they think of you. If you're not already doing it, you may want to seek out outside--help, e.g., OT and reading and handwriting tutors. Yes, it gets expensive but I would not rely solely on the school to give him the help he needs. (They won't.) Check to find out what you can get reimbursed for and possibly set up a medical savings account.
Also, 18:18--pls don't post your experience with your NT kid. This child most likely has a learning disability+ whether or not it is acknowledged by the county. No amount of legos will change it.
16:36--yes muscle control can improve with lots of work over time but my kid is going on 5 years of OT--sometimes it's been 4x a week, now 2x a week--that is of little comfort. Also, so many kids have additional lds related to executive functioning on top of the low muscle tone that handwriting can be the least of their worries.