I think you have given the principal a chance - the next step in "honoring the chain-of-command" is to move it up the food chain. I would forward the principal's recent email and a copy of your report with diagnosis and evaluations to central office. Tonight. I would look at your district website and find the director of special Ed, director of special services or director of Pupil Personnel Services. I would reference the prior agreement but only forward the other emails if this person balks at putting a 504 in place.
In second grade my DD (with a laundry list of LD diagnoses including dysgraphia and dyslexia) averaged only 70% when she had to write her spelling tests herself, *above 95%* when she could do them orally. This accommodation was in her IEP all year but it was hard to get the teacher to understand and implement her accommodations. Getting the 504 in place will be a start - it may still take time to get everything worked out and implemented.
I am confident this will work out. And no this is definitely not one I would just let go. If he is dysgraphic his challenges are likely to get worse - you want to get things in place now.
Good luck!
