A comment on my last post mentioned that lots of boys seem to claim to have physical pain when they write.
Ralph Fletcher also mentions this phenomenon in his book "Boy Writers" (without adding any suggestions for a solution.)
Our boy has occasionally mentioned his hand was tired, but hasn't done so lately. However, when I watch him write, it becomes clear that he pushes the pencil very hard on the paper. It's hard for him to use a mechanical pencil, for example, because the leads always break.
When I am helping him with homework, I always am telling him to write gently and not to push as hard.
I don't know how many boys who claim hand pain are being overly aggressive with their pencils, but that might account for some of it.
As for our boy, the problem has usually been that he can't think of anything to write. Today, however, he was all excited to get to school so he could finish the book he was working on.