Should I stay or should I go?

My son, the seventh grader, is doing more and more of his homework completely on his own. We have to nag him to his workspace at the kitchen table, but once he's there, he does a pretty good job of working independently. Which is great! Except that his writing is messy, and his teacher would like it to be neater. So she writes notes asking that we tell him to take his time and write slowly. Which you have to do constantly or you get one neat word and a mess after. But if we sit with him and prompt him and prompt him to write neatly, he's not working alone. And maybe, sometimes, because it's hard to just sit there and watch mistakes being made, we correct his work, too. So the work that goes to school is neat and also correct. Much more correct than the work he does at school. So the teacher writes notes asking us to make sure he does his work alone. Which he does. Which is great! Except that his writing is messy. You see where I'm going with this. As far as I can see, the teacher has two options: Messy writing done independently, or neat writing done with Mom or Dad hanging over shoulder. Personally, I'd opt for the former. But opt she must.