It's awesome that your son's teachers are letting him keyboard. When my 'summer birthday' boy had his first official grade skip into a private school with higher than average 'output demands' the writing was an issue. Both because his hands hurt, and also because he was embarrassed to have little-kid-looking paper. Also because keeping track of what he wanted to say+writing it by hand+grammar and spelling was too much, and, I think, led to him really squeezing that pencil.
Given my personality, I went to the private school INSISTING, that they treat him 'as if' he had dysgraphia. They even let him 'annotate his literature book' on a spreadsheet. And so he didn't write for 2 years. During that time we spent 3 15 minute sessions with 'Handwriting without tears' so that DS could intellectually break down the components to 'pretty writing.' Toward the end of the 7th grade, they taught 'note taking' as a skill. He came home with beautiful handwritten notes, and has been able to 'write pretty' at will ever since.
Of course in High School the teachers want the assignments typed, and even collect them digitally so they can be checked for cheating.
So my advice would be hot house typing if necessary and not worry about even the 'minimal amount of writing.' If you have a wonderful professional, sure, a trip to rule out any physical problems is probably worth the hassle.
Best Wishes,
Grinity
