It really doesn't matter what is causing the problem, whether it's the brain or the hand - he's got a problem. The Occupational Therapist (OT) can help diagnose and depending on what she finds and what she says can be done to alleviate it, he could be in line for use of a keyboard. Because even if it's just clumsiness, or even dyslexia, a keyboard makes it easier.
In this, the US and Australia are almost identical. The train of events - get an Occupational Therapist (OT) to assess. Not only with the Occupational Therapist (OT) look at how his hands function, she will also assess any pain, mobility issues (range of movement), maybe prescribe exercises (although if it's just for assessment she mightn't go so far as such recommendations) and do a timed test of him hand-writing, and typing. Legibility will come into it a bit, but if he is demonstrably faster at typing and the Occupational Therapist (OT) also diagnoses a problem with hands, then the recommendation is made to the school (or board of studies, or whoever) to get him onto a keyboard for writing tasks.
The keyboard generally recommended is Alphasmart Neo. It's a cute little thing, about the size of a computer keyboard alone and rounded a bit at the top to allow for a small screen which displays about two lines of text. It can hold about 9 text files as a maximum. Battery-powered, seems to run on thin air. Fits neatly into a briefcase, is fairly tough.
The best thing about it - you can download the text files into any computer, Mac or easy child. It downloads as a text file, all formatting has to be done on the computer. But since the main task is text, this is OK. You should always do the pretty stuff afterwards anyway.
difficult child 3 has had one since Year 4. Because it was from the Board of Studies, it changed schools when he did. When he left mainstream for state-based correspondence, the Alphasmart came too. It still belongs to the Dept of Ed, but difficult child 3 has the use of it.
Exams - he has to first demonstrate that every file is empty (no saved text anywhere) and then he does the same paper as everyone else, but he types his answers into the Alphasmart in one long text file. After the exam, he goes with the teacher to download his work onto the teacher's computer. We carry a USB cable in the briefcase with the Alphasmart.
When we've gone on holidays during school term, we take the Alphasmart with us. That's because he's a correspondence student and we have it at home with us. For a mainstream kid, the Alphasmart stays in the classroom. But on holidays in the car, difficult child 3 has been able to keep a diary of where we go and what we do, later on he transfers the text file to a computer and adds in photos, formats it all and sends it off to his teachers.
difficult child 3's handwriting is shocking. He also can't draw for peanuts. Neither can difficult child 1. easy child 2/difficult child 2 has neat handwriting, but she shares with the boys problems with sore hands when writing. With our kids, the problem is hypermobile joints.
difficult child 3's handwriting used to be much more legible, but it was never great. We always knew about the loose joints - when you see a kid bend his fingers back as far as he did, and see his fingers bend outwards on the tips when they should be curling in for a pencil grip, you know he has problems. The Alphasmart has made all this so much easier.
Frankly, we live in an era where tidy handwriting is far less necessary than ever before. If all else fails, make sure he becomes a doctor.