L.R.
Work with his teacher to figure out one important thing: Is the problem his ability to get concepts onto paper, or is the problem the physical act of writing itself? It can be either or a combination of the two. If the problem is the act of writing, talk to the teacher about how to proceed and whether he should be evaluated by and work with an occupational therapist. (My friend's son was convinced he couldn't write, but once an OT evaluated him and started therapy with him, he improved a great deal and realized he could indeed get his great ideas into written words and his hands didn't have to "get in the way" of that!)
If the issue instead is getting the ideas he can think and speak onto paper, ask the teacher for some exercises, beyond his usual homework, to help him. The school may have access to specialists who can work with him during the school day until he's over this hurdle. It's fairly typical for some kids to have a tough time with getting words onto paper, whatever the reason, around first-second grade, so don't panic, but do work with him and the teacher on it now. By third grade and up he'll be expected to do much more on his own so this is a good year to help him through it.